Disinfectants: Harm From the Cure
Chemical Hazards vs. Biohazards
© Paul Robbins 2022
In this Article…
Least-Toxic Commercial Disinfectant Products
Using Vinegar as a Disinfectant
History of Vinegar As a Disinfectant
Proof of Disinfectant Effectiveness
When NOT to Use Vinegar
Kitchen Kemistry: Cleaning Recipes Using Vinegar
Ultraviolet Light As a Germ Killer
UVGI (UV Germicidal Irradiation) Product Types
Far UV-C Safety
UV-C Disinfectant Products
Thanks to Wendy Nine and Gail Vittori for proofreading this article.
Courtesy Pixabay, PhilEnder
Since the rise of the COVID-19 pandemic in early 2020, the world has been obsessed with disinfectants. While increased use has likely saved numerous lives, the increased use of this class of products has also endangered them.
Due to the pandemic, between 2019 and 2020, there has been a profoundly steep increase in poisonings in the U.S. related to various type of disinfectant products:
- A 57% increase in poisonings from residential disinfectant use (from 10,970 to 17,181);
- A 59% increase in poisonings related to industrial disinfectant use (from 1,320 to 2,104);
- A 22% increase in poisonings related to residential bleach use (from 34,304 to 41,977);
- A 62% increase in hand sanitizer poisonings (from 21,051 to 34,170).
One reason for this spike is that many people are unfamiliar with how to use them safely. In a 2020 survey of the U.S. population conducted by the Center for Disease Control and Prevention, 39% of respondents reported engaging in high-risk disinfection practices during the COVID-19 pandemic.
These included: application of bleach to food items such as fruits and vegetables (19%); use of household cleaning and disinfectant products on hands or skin (18%); misting the body with a cleaning or disinfectant spray (10%); inhalation of vapors from household cleaners or disinfectants (6%); and drinking or gargling diluted bleach solutions, soapy water, and other cleaning and disinfectant solutions (4% each).
CDC survey showing high-risk cleaning and disinfection practices
Literally 25% of respondents reported at least one adverse health effect during the previous month they believed had resulted from using these cleaners or disinfectants, including: nose or sinus irritation (11%); skin irritation (8%); eye irritation (8%); dizziness, lightheadedness, or headache (8%); upset stomach or nausea (6%); or breathing problems (6%).
These are just the short-term dangers. Long-term, some of ingredients in these biocides are extremely harmful.
Below is an analysis of a sample of the more toxic ingredients in some of the more questionable disinfectant products on the U.S. market as of January 20, 2022.
Least-Toxic Commercial Disinfectant Products
Product alternatives to these toxic ingredients are based on more benign substitutes. They include: Citric acid, Hydrogen peroxide, Hypochlorous acid, L-Lactic acid, and Sodium dichloroisocyanurate. A suggested list of safer name-brand disinfectants has been complied by the Toxic Use Reduction Initiative (TURI) at the University of Massachusetts. It is found at this link.
(TURI also recommends a few products that include ethanol, which can be carcinogenic if ingested.)
Vinegar as a Disinfectant
The Salad Dressing That Kills Germs
HollyHarry / Shutterstock
Vinegar, a.k.a. acetic acid, is a chemical derived from fermentation of the (already fermented) chemical ethanol. While primarily used in food preparation, it has a history as a disinfectant going back thousands of years.
History of Vinegar As a Disinfectant
The antiseptic properties of vinegar have been known for thousands of years.
By legend, it was used as a food preservative in Babylonia as far back as 5,000 BC.
The pioneer physician Hippocrates used it to treat wounds and ulcers circa 420 BC.
In the 1st century AD, Aulus Cornelius Celsus, who authored one of the best historical documentations of health and medicine in the Roman Empire, recommended vinegar for disinfection of abdominal wounds.
Karl Friedrich Meyer’s classic book Disinfected Mail (1962) reported finding a letter dated 1485 which had apparently been disinfected with vinegar.
Antonie Van Leeuwenhoek, the 17th century pioneer in microbiology, offered the first scientific proof of the action of acids on microorganisms. He observed that, under a microscope, bacteria ceased activity when covered with wine vinegar. There were also recommendations by several doctors and veterinarians in the 17th and 18th centuries for use of vinegar as an ingredient to fight cattle plague.
Vinegar was used during WW1 for wound disinfection.
In reports from 1916-17, it was discovered reported that a 1% concentration of acetic acid in saline cured Pseudomanas aeruginosa wound infections.
Proof of Disinfectant Effectiveness
More Than an Urban Legend
More recently scientific studies have actually measured vinegar’s effectiveness at killing microbes. They are quantified it in terms of scientific standards used in health-care and food processing: log scale.
The disinfection standard for critical facilities in the U.S. such as hospitals, where 6-log, a 99.9999% reduction in less than 10 minutes, is required due to the exponential rate that microorganisms can reproduce. While this standard may seem obsessive, microbes multiply at exponential rates in a very short time period, justifying their almost-complete eradication in health-related settings. Just one microbe that doubles in 20 minutes can multiply to 1.1 trillion in about 10 hours.
Starting from a base of 10,000,000 microbes, a 1-log (90% reduction) is 1,000,000 microbes. 2-log (99% reduction) is 100,000 microbes. At 7-log (99.99999%), there is a single microbe left.
The U.S. Environmental Protection Agency maintains a lower standard for food contact surfaces of ≥5-log for bacteria and ≥ 3-log for viruses, and ≥5-log for non-food contact surface disinfection for bacteria.
Log Scale is the standard for microbe eradication in health-care and food processing professions.
- In 2020, a detailed study from Germany analyzed the germ and virus reducing properties of vinegar and citric acid. It found varying but marked reductions in all cases when tested against 9 types of bacteria, mold, and virus systems. Most of these micro-organisms caused disease or infections including: pneumonia; blood poisoning; gastrointestinal problems; sinus infections and other respiratory illness; and bone, urinary and heart-valve infections.
The study evaluated the use of purified vinegar by itself or in combination with citric acid, at various concentrations: 5% acetic acid; 7.5% acetic acid; 10% acetic acid; and combination of 10% acetic acid and 1.5% citric acid.
Depending on the organism and acid concentration, all the organisms were completely eliminated, except for Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA), in a suspension test. Even then, a high level of reduction was achieved for Staphylococcus aureus (4.75-log, or 99.998% reduction), and MRSA (3.19-log, or a 99.935% reduction).
Log Reduction for various bacteria in suspension tests. The different reductions were obtained due to different initial loads. [+] indicates a complete reduction of the microbial load.
Source: Marc-Kevin Zinn and Dirk Bockmühl, “Did granny know best?”
In another test in this study that evaluated disinfection effectiveness in clothes washing for 5 microorganisms exposed to 0.75% acetic acid added to detergent in wash water, only staph was not completely eliminated, and even then, a high rate of reduction was observed (5.8-log, a 99.99984% reduction). This volume of vinegar would be equal to 4/10ths of a gallon of 5% common cleaning vinegar in a washing machine that consumes 2.6 gallons per load, roughly a 1-to-6 ratio of vinegar to water.
Log Reduction of various bacteria after a simulated main wash cycle (60 min at 30 °C) in the Rotawash using liquid detergent. A washing cycle without addition of acetic acid, a wash cycle with addition of 0.3%L acetic acid and a wash cycle using 0.75% acetic acid. The different values for LR max [+] (indicating a complete reduction of the microbial load) were obtained due to different initial loads.
Source: Marc-Kevin Zinn and Dirk Bockmühl, “Did granny know best?”
- A British study from 2010 assessed the disinfection of various household products on an influenza virus. It determined that 10% malt vinegar could virtually eliminate infectiousness almost instantaneously. A mixture of water with a 1% bleach, or a mixture of water with as little as 0.01% dish washing detergent, could have the same effect.
- A 2015 study from the University of Massachusetts–Lowell showed that a Do-It-Yourself home cleaner consisting of about half fresh (carbonated) club soda, half vinegar (at 5% strength) and a dash (0.02%) of tea tree oil was close to the effectiveness of bleach solution on two kinds of common bacteria at close to 6-log potency.
- A Japanese study from 1997 recorded the bactericidal effectiveness of vinegar in a suspension test of 17 different strains of food-borne pathogens. It determined that 0.1% concentration of acetic acid eliminated visually-observed bacteria in a day. Common table salt in conjuncture with vinegar enhanced the effectiveness, and glucose enhanced the effectiveness in all but one of the pathogens (where the effectiveness actually decreased). It also found that high temperatures enhanced effectiveness. In one case, a 3-log reduction in bacteria reduction from vinegar took place in less than a minute at 50 degrees C, while the same rate took more than 75 hours at 10 degrees C.
Another important point in this paper was that it was not just the acidic nature of vinegar that renders it effective. Researchers could not replicate the results when they used hydrochloric acid as an alternative.
- A 2014 study of vinegar’s effects on a class of bacteria highly resistant to disinfectants (mycobacteria, including tuberculosis) found that vinegar with an acetic acid concentration of at least 5% could eradicate various of these bacteria when exposed for 20 to 30 minutes. Of the 10 different bacteria, almost all of them were reduced by a level of 3-log to 8-log.
The 20-30 minute time required is longer than the 5 minutes recommended for some commercial products. However, the general standard for effectiveness in mycobacteria disinfectants is 4-log or 5-log, which was sometimes surpassed by higher vinegar concentrations.
- A 2021 study from the U.K. evaluated the effectiveness of apple cider vinegar. It found: 1) restricted colony growth occurred in 2 different antibiotic-resistant bacteria in concentrations as low as 0.5% acetic acid; 2) at the same time antimicrobial action took place, the vinegar increased white blood cell counts; 3) different acids (hydrochloric and sulfuric) did not have the same effect. The paper observed that one reason for the antimicrobial effect was the reduction of key proteins in the bacteria.
- A Spanish study in 2006 tested various foods reputed to act as bactericides. Common foods, ingredients in various food products, and beverages were scrutinized for their antimicrobial properties against 6 different bacteria that induced food poisoning. It found that vinegar in mayonnaise and salads reduced these pathogens to undetectable levels in some cases and had a 5-log reduction in others. (The study also found that (depending on the context) virgin olive oil, sometimes alone and sometimes mixed with lemon juice, eliminated or greatly reduced certain bacteria.)
- A Korean study from 2021 compared the effectiveness of acetic acid to sodium hypochlorite (which is a more dangerous chemical) to control 7 food pathogens that could grow in spite of cold temperatures typical in the food processing industry. It concluded that acetic acid at concentration of less than 1% may be the more effective chemical to inhibit growth.
- A 2015 study from scientists in Birmingham, U.K. found that vinegar inhibited the growth of 29 pathogens associated with wounds from burns at concentrations of only 0.16 to 0.31%. This was held as an alternative to the waning effectiveness of antibiotics.
- Of all the studies reviewed for this article, the one that cast the most skepticism on vinegar’s disinfectant qualities was from the University of North Carolina. The paper, issued in 2000, compared effectiveness of various commercial brand-named hospital and household disinfectants, as well as vinegar (5%) on 8 bacteria of concern, as well as poliovirus.
Microorganism reductions were measured at both half-minute and 5-minute intervals. The study found vinegar comparatively ineffective on 5 of these bacteria and the virus. But it did find it effective above 5-log or 6-log on two of the bacteria (sometimes surpassing results in commercial products) at both time intervals, and above 5-log in a third bacteria after a 5-minute treatment (again sometimes surpassing commercial products).
Where NOT to Use Vinegar
While the beneficial properties of vinegar can often enhance the attributes of other cleaning ingredients, do not mix it with chlorine bleach or hydrogen peroxide. Mixing with chlorine bleach can create dangerous chlorine gas. Mixing it with hydrogen peroxide can create harmful peracetic acid.
And while vinegar is a good general cleaner for most things, avoid certain uses:
• Delicate fabrics (if worried, test a small sample);
• Dishwasher, clothes washer, and appliance seals and hoses made of synthetic rubber (check with manufacturer or manual to determine if it can be used);
• Electronic touchscreens;
• Natural stone (e.g., granite) countertops and stone flooring (the acid can etch the surface);
• Tile grout.
Kitchen Kemistry: Cleaning Recipes Using Vinegar
The “science” of vinegar and baking soda • Courtesy katerha, Wiki Commons
Being a strong acid and disinfectant, vinegar can serve as replacement for toxic commercial cleaning products for a variety of uses. A list of practical ideas and recipes is presented here.
Thanks to sources: Clean & Green, Annie Berthold-Bond, Ceres Press (1990); and “Healthy Indoor Air Savings,” Foundation Communities (Austin, TX), online at this link.
|Cleaning Recipes Using Vinegar|
|All-purpose Vinegar Spray Cleaner – Add 1 to 4 mixture of vinegar to water. Add drops of essential oil if desired. Shake before each use.|
|Glass – Remove ugly film in narrow-necked glass jars, flower vases, and bottles by letting undiluted white distilled vinegar sit in them for a few hours. Add a little rice or sand and shake vigorously to loosen stubborn stains. Repeat if necessary.|
|Hands – Wipe your hands with vinegar to remove strong scents like onion and garlic.|
|Metal Cleaner (General) – Make a paste with vinegar and 2 tablespoons cream of tartar.|
|Metal Cleaner (Brass & Copper) – Make a paste with vinegar and 3 tablespoons of salt.|
|Metal Cleaner (Brass & Copper) – Mix 2 parts vinegar with 2 parts lemon juice.|
|Metal Cleaner (Chrome) – saturate sponge with 1/8 cup of cider vinegar.|
|Metal Cleaner (Iron) – Make a paste with vinegar and 3 tablespoons of alum.|
|Window cleaner – 1 part vinegar to 8 parts water in spray bottle.|
|Drain Maintenance – Pour 1/2 cup of baking soda down drain, followed by 1/2 cup vinegar. Let sit for 15 minutes, and rinse with hot water.|
|Germs – Spray with full-strength vinegar. You can wipe dry, but more effective when it dries by evaporation.|
|Grout – Let full-strength vinegar sit on it for a few minutes and scrub it with an old toothbrush.|
|Metal Sinks – Stainless steel sinks will shine after you clean with a mixture of baking soda and vinegar.|
|Mineral Build-up – 1/4 cup vinegar and 1 tablespoon alum.|
|Mildew – Spray shower walls and shower curtain with half vinegar and half water to help prevent mildew.|
|Mildew & Soap Scum – Wipe with vinegar then rinse.|
|Odors – Place a bowl of vinegar in the room overnight.|
|Toilets – Pour in a cup or more of vinegar and let it sit several hours or overnight. Scrub well and flush.|
|Dusting – Use spray bottle filled with half vinegar, half water and lightly spray a rag to dust all surfaces.|
|Dusting – 1/2 teaspoon olive oil, 1/4 cup vinegar, soft cloth.|
|Cleaning – 1/4 cup vinegar, warm water, 1/2 teaspoon vegetable-oil based liquid soap.|
|Carpet Cleaning – 1/4 cup vinegar, 1/8 cup salt. Rub on carpet with sponge. Let dry. Vacuum.|
|Carpet Stain Remover – 1/4 cup vinegar, 1/4 cup water. Sponge on and rinse with water.|
|Carpet Stain Remover – 1/4 cup vinegar, 1/2 cup water, 1 teaspoon vegetable-based liquid soap. Rub into stains and rinse with water.|
|Floor Wax Remover – 1/4 cup vinegar, water, washing soda. Cover floor and let dry completely before rubbing off.|
|Polishing – 1/8 cup vinegar, 1/4 cup lemon juice, 1/8 cup food-grade linseed oil, few drops Vitamin E as preservative.|
|Polishing – 1/4 cup vinegar, 1/4 cup olive oil, 2 drops of essential oil for scent.|
|Polish Remover – vinegar and water.|
|Wood – Remove water rings with a solution of equal parts vinegar and vegetable oil. Rub with the grain.|
|Counter Tops – Clean with a rag and vinegar.|
|Cutting boards – Wipe wooden boards with vinegar.|
|Dishwasher – Pour a cup of vinegar inside an empty machine and run through a cycle.|
|Grease – Use a sponge soaked in vinegar.|
|Microwave – Mixing equal parts vinegar and water in a microwave-safe bowl. Bring it to a boil inside the microwave. Wipe clean.|
|Plastic Food Containers – Wipe with a cloth dampened with vinegar to remove stains and smells|
|Refrigerator – Clean with a solution of one- part water and one-part vinegar.|
|Spot Away – Add 1 to 2 tablespoons of vinegar to dish water|
Ultraviolet Light As a Germ Killer
The Disinfectant from Outer Space
Ultraviolet light (UV) is a longstanding non-chemical disinfection technology. Certain kinds of UV have strong antimicrobial properties. For over a century, it has been created by artificial lamps that replicate UV originally contained in sunlight at the edge of the Earth’s atmosphere.
Ultraviolet light is the band of energy below the visible blue/violet spectrum, and is undetectable to the human eye. There are generally 5 categories of it, measured in frequency units or nanometers (nm).
Courtesy UV Resources
UV-A occurs in sunlight between 315 and 400 nm. Its commercial applications include: auto-fluid leak detection; “black lights” for decorative purposes; curing lamps for plastics, paint, and printer’s inks; detection lamps for currency forgeries; insect-attracting light bulbs for bug-zappers; mice and scorpion detection; stain detection for furniture and flooring; and sun tan light tubes. UVA has disinfectant qualities, but they are extremely limited compared to some other UV categories.
UV-B also occurs in sunlight, but in the band between 280 and 315 nm; 95% of it is screened out by the Earth’s protective atmosphere.
Some UV-B is essential for health. In humans and other animals, UV-B in sunlight contacting skin creates calciferol, a hormone also referred to as “Vitamin D” that allows the body to metabolize calcium. At various levels of exposure, it can create sun tan, sun burn, and sometimes (in the case of chronic overexposure) skin cancer. Commercially, UVB’s uses include: sun tan light tubes; treatment of certain skin disorders; and lighting supplements for indoor reptile environments (such as zoos).
UV-C refers to light between 200 and 280 nm. It is currently used for disinfection of air, water, indoor surfaces, food, and medical equipment.
In nature, UV-C is almost entirely filtered out of sunlight by the Earth’s atmosphere. For practical disinfectant uses, it is only available on Earth via artificial lamps that replicate its frequencies. Since small microbes (bacteria, fungi, viruses, yeast) are not generally exposed to UV-C, they have no natural resistance. UV-C light will penetrate the thin cell walls of microbes and damage their DNA, making it difficult or impossible to survive and multiply. Its germicidal effects have been known, to some degree, since the late-19th century.
Within the UV-C band are 2 smaller bands.
- Near UV-C refers to light between 230 and 280 nm. It has pronounced antimicrobial properties. However, it can also damage human skin and eyes. For this reason, antimicrobial Near UVC must be used in uninhabited areas, or located to avoid direct exposures, or with skin and eye protection.
- Far UV-C refers to light between 200 and 240 nm. It also has strong antimicrobial properties, though not as strong as near UVC. However, since frequency is not as strong, the harm to skin and eyes is greatly reduced or non-existent.
UV-A, UV-B, and UV-C can all cause degradation of certain materials such as plastic and rubber. Far UV-C is probably the least harmful since it has less ability to penetrate.
UV-V or Vacuum UV, between 100 and 200 nm, is so named because it can only pass through a vacuum, such as space outside of the Earth’s atmosphere. It is virtually undetectable on the Earth itself. Commercially, artificially created UV-V is used for ozone generation to eliminate odors and toxins in indoor air, as well as high-tech lasers and nanotechnology.
The healing power of the sun has been known to the Earth’s major civilizations for thousands of years.
In the 5th century BCE, the pioneering Greek physician Hippocrates prescribed heliotherapy (sunbathing) for medical and psychological ailments. It was discussed in the writings of various Greek and Roman scholars between the 5th century BCE and the fourth century CE. It reappeared during the Middle Ages, documented by the Persian physician Avicenna in the 11th century CE.
In 1876, French scientist G. Ponza used light therapy to treat mental illness, finding UV effective at reducing mania, while red light improved depression. Today, phototherapy is considered essential in treating what is diagnosed as “Seasonal Affective Disorder,” (SAD) which leaves some people severely depressed when winter shortens the number of daylight hours.
In 1920, Swiss physician Auguste Rollier observed that sun treatment was associated with increased white blood cell production, which boosted the immune system. Later, in his 1923 book Heliotherapy, he discussed Alpine sunbaths to cure wounds and surgical (extra-pulmonary) tuberculosis.
Light was also used to treat eye disease. Around the turn of the 20th century, Nesnamov, a Ukrainian university teacher, used sunlight to treat corneal ulcers. In 1922, another university instructor, Dr. Felisa Nicolås, reported that sunlight treated conjunctival tuberculosis. A German doctor, Fritz Schanz confirmed Nicolas’ results and also proved that eyelid eczema was treatable with light. In 1923, J.W. Wright, an American ophthalmologist, recommended sunlight or artificial light to treat other eye-related problems.
Several turn-of-the-20th-century scientists used red light to reduce the severity and duration of scarlet fever and skin inflammation.
However, scientists also documented adverse health effects from light, at least too much of it, including rashes, sunburn, and skin cancer.
The Discovery of UV Light
In 1801, the phenomenon of UV light itself was probably first discovered by Johann Wilhelm Ritter, a German medical teacher. While it had earlier been proven that paper soaked in silver chloride would darken when exposed to sunlight, he found that the chemically-treated paper was even more affected by the violet end of the spectrum. Eventually the term “chemical rays” was adopted to describe UV because of the observation.
Actual disinfectant properties of UV were recognized later in the 19th century.
- In 1877, British scientists Arthur Downes and Thomas Blunt observed that test tubes with a medium that would support bacteria remained germ-free when exposed to sunlight. They later discovered that the effectiveness of this method was determined by dose.
- Considerable attention was given to UV light by physician Niels Ryberg Finsen, who discovered a UV cure for skin tuberculosis. He began treatments in 1896, and by 1902, had observed improvements of almost 90% of 802 patients. He received a Nobel prize for his work in 1903.
UV Treatment with “Finsen Lamp,” London, 1925, Wiki Commons
- In 1904-1905, German ophthalmologist Ernst Hertel showed that UV-C was more effective at disinfection than UV-B, and that UV-B was more effective than UV-A.
- In 1907, German researchers K.A. Hasselbalch and H. Jacobaus employed UV to treat cardiac afflictions.
- By 1924, American physician Alfred Fabian Hess determine that cod liver oil or exposure to UV prevented rickets, and certain foods could treat rickets after the foods were exposure to UV. He determined that ergocalciferol (Vitamin D2) could be used in the same way, and co-shared a Nobel Prize in chemistry for the discovery in 1928.
- At the same time, another American physician, Harry Steenbock irradiated food with Vitamin D and cured rodents of rickets, going on to patent the invention that was used in food processing.
- In 1926, Sir William Stewart Duke-Elder, a Scottish ophthalmologist, reported that UV rays were effective treatment for various eye problems.
Commercial Use of UV for Water Disinfection
- In 1910, the first large UV water disinfection system was established in Marseilles, France. But it closed shortly after opening because of technical problems with the nascent technology. Chlorine disinfection was introduced in the 1920s. Since it was cheaper and more reliable, chemical treatment became the standard, and UV was ignored for several decades.
- In 1955, the first installations of more modern and reliable UV water treatment facilities occurred in Austria and Switzerland. Norway began to adopt it in 1975. By 1985, there were over 1,500 UV installations at European treatment plants; by 2001, there were over 6,000.
- In 1978, UV disinfection was installed at a wastewater treatment plant in Waldwick, NJ, the first such reported use in the U.S. In 2016, the City of Chicago opened a wastewater treatment facility, at that time considered the world’s largest that was augmented by UV.
- In 1998, James R. Bolton and his co-researchers found UV highly effective against Cryptosporidium and Giardia, which are chlorine tolerant. This led to the beginning of its use to augment water treatment. In 2012, New York City commissioned a UV water treatment facility.
Commercial Use of UV for Air and Surface Disinfection
Commercially produced UV lamps began to be produced in the U.S. in the 1930s. Between 1945 and 1947, their use increased to disinfect air in hospitals and food-associated applications such including meat processing and storage, bakeries, breweries, dairies, and kitchens. In the 1950s, UV began to be used in HVAC systems.
- In 1936, Dr. Deryl Hart of Duke University’s Dept. of Surgery installed UV in the operating room at Duke University Hospital. UV reduced post-operative wound infection from 11.62% (control) to 0.24%. Subsequently, other hospitals began to employ UV with similar success.
- Between 1937-1941, U.S. scientist and sanitary engineer William Wells and colleagues demonstrated the concept of upper room UV disinfection (described in more detail below) in Philadelphia schools prevented a measles epidemic where infection outside the schools was unlikely. UV successfully reduced the rate from 53.6% (control) to 13.3%.
- In 1941, doctors Fé Del Del Mundo and Charles McKhann installed UV “light curtains” as barriers to prevent respiratory cross infections at the Infants’ Hospital of Boston. UV successfully reduced the rate from 12.5% (control) to 2.7%.
- In 1957, upper-room UV technology was used to control influenza in a hospital, successfully reducing inflections from 18.9% (control) to 1.9%. In the 1950s and early 1960s, ventilation ducts exposed guinea pigs to air from a TB ward. However, the air in one of the ducts was treated with UV. The experiment showed a deactivation rate of 100%.
Despite these positive results from these and numerous other studies, universal acceptance of UV-C disinfection alternatives was considerably delayed. Because of different methodology and context, the successful results could not always be duplicated. Antibiotics were developed to treat TB. And there were concerns about UV health effects to skin and eyes, as well as ozone unintentionally emitted from earlier versions of the lamps.
However, beginning in 1997, indoor use of UV for disinfection began a resurgence as antibiotic-resistance strains of tuberculosis began to appear. Scientific studies were conducted in various U.S. cities to determine the technology’s effectiveness at controlling the disease.
By 2003, the U.S. Center for Disease Control and Prevention acknowledged that UV-C could serve as a supplemental air cleaning measure for bacteria and virus control in hospitals. The same year, UV was used to prevent the spread of SARs viruses in the air of Chinese hospitals. Also in 2003, the U.S. Federal Emergency Management Agency recommended it for protection and mitigation of bioterrorism.
In 2004, UV-C use was expanded to disinfect SARs from Chinese banknotes.
Since then, UV-C use for disinfection became commonplace. Then in 2020, as the COVID-19 pandemic became a dominant feature in daily life, managers of commercial buildings, mass-transit vehicles such as airplanes, trains, and buses, as well as individuals, began looking to UV as another strategy of protection. However, there were concerns about its safety to exposed individuals.
UVGI (UV Germicidal Irradiation) Product Types
When all uses of UV disinfection (health care, buildings, food, water) are considered, the world’s UV market is considerable. A 2022 report by Global Industry Analysts, Inc. estimated the year’s sales at $4.7 billion. The major categories of UV products are described here to give readers a sense of their multifaceted uses.
Upper Room Air Disinfection Systems
Courtesy UV Resources
One of the most common uses of UV in buildings employs lamps mounted towards the top of a room to disinfect air. The strategic mounting prevents direct exposure to skin and eyes from Near UV-C. If the air is well circulated so that it is continually exposed to the light source (via supply ducts and/or ceiling fans), it can be highly effective in disinfecting air. These units have been used extensively to mitigate the spread of airborne tuberculosis.
The image below shows two configurations of these systems. In rooms with higher ceilings, the lamp is pointed upwards to reflect off the ceiling. With lower ceilings, the units should be louvered for the room occupants’ protection. Both strategies prevent UV-C exposure to skin and eyes.
Germicidal lamps for air disinfection in occupied rooms: (a) open unit used in rooms over 10 ft in height; (b) louvered unit used where ceilings are lower than 10 ft. Dimensions: A, 20 ft; B, 10 ft; C, 7 ft; D, 10 ft. (Illuminating Engineering Society, The Lighting Handbook, 2011)
HVAC Air and Internal Cabinet Disinfection Systems
These systems are installed in HVAC ducts near cooling coils to prevent mold and bacteria enabled by condensation, or near the air handling unit to disinfect return air. They are not nearly as effective as upper-room air systems at disinfecting large spaces, but can prevent problems in hard to reach places such as air conditioning coils.
Courtesy UV Resources
In some cases, Near UV-C can cause degradation of HVAC filters over time.
Small Room Air Disinfection Systems
These portable systems contain both a High Efficiency Particulate Air (HEPA) filter and a UVGI lamp inside an enclosed container. They are not nearly as effective as upper-air systems, and are, in general, intended for small enclosed areas (e.g., rooms 200 square feet or less).
Bare-Lamp Fixed or Portable Air and Surface Disinfection Systems
L-VIRA, a germ-zapping robot, emits a flash of UV-C light in a hospital room at William Beaumont Army Medical Center. The UV-C destroys cells within a certain radius and reducing the number of Healthcare Associated Infections in the area. Note that most UV rays do not penetrate glass or plastic. Photo by Marcy Sanchez, Wiki Commons.
Unlike upper-room disinfection systems, HVAC, and small room disinfection systems, bare-lamp systems expose room air and (unshaded) surfaces directly to UV-C. There are a number of variations on this approach.
- Some are permanently mounted on the wall or ceiling.
- Others are physically placed in an area intended for disinfection (similar to a table lamp).
- Still others use robots that move the UV source through a larger room area, transit bus, or airplane, disinfecting an immediate area of the space as it travels.
If these units use Near UV-C, the space must be evacuated of people, animals, and plants to avoid possible harm. As extra measures of protection, many of these units employ: 1) timers that allow people to leave for a designated time period while the disinfection process is underway; 2) remote control to allow the operators switch on units after they have left the space being disinfected; 3) occupancy sensors that turn the systems off when a person enters the room during disinfection.
In some cases, UV-C can cause degradation of materials in the room such as paint and yellow plastics over time.
Hand-Held UV Emitters for Surface Disinfection
There are various types of hand-held UV emitters that disinfect as they are held over surfaces for sufficient periods of time.
These range from “wands” that are only 5 inches long meant to disinfect small objects (phones, keyboards) to industrial sized units more than 2 feet long.
If Near UV-C lamps are used, this equipment usually requires the operators to wear protective clothing and glasses. Some will not operate unless the lamp is held downward in order protect workers and building occupants.
Hand-Held Vacuum Cleaners for Surface Dust Removal and Disinfection
Another type of handheld disinfectant product is HEPA vacuum cleaners that contain UV-C lamps on the underside. These are particularly useful for cleaning and disinfecting bedding, upholstery, and some fabrics.
Enclosed-Container Disinfection Systems for Small Objects
Various UV disinfection products use enclosed boxes, bags, and cabinets with a UV lamp inside to disinfect small items that frequently come into human contact. The products allow disinfection with Near UV-C without the worry of skin and eye exposure. Items that can be treated include medical masks, keyboards, phones, and even shoes and toothbrushes.
Water Disinfection Systems
Products and equipment using UV disinfection run the gamut, from home systems that augment water filters to water purification of rainwater collection to commercial systems for municipal water and wastewater treatment. There are thousands of regional water and wastewater systems throughout the world that use UV to treat water or wastewater.
UV wastewater treatment has the advantage of replacing conventional chlorine disinfection. Chlorine is problematic because of its toxicity to aquatic life. The chemical also combines with carbonaceous materials in water bodies it is released into (e.g., decaying plants), creating trihalomethanes that are toxic to humans and wildlife. Both New York City and Chicago employ the technology for some of the largest UV wastewater treatment plants in the world.
This picture from the O’Brien Water Reclamation Plant in Illinois shows 896 UV lamps shining in a pool of water to kill harmful bacteria and pathogens. The water is then released from into the Chicago River. Photo from Metropolitan Reclamation District of Greater Chicago.
At the residential level, according to a 2021 survey conducted by the Water Quality Association, 22% of U.S. homes have a “Point-of-Use” whole-house water filter system. A noticeable percentage of these use UV disinfection.
Food Disinfection Systems
Spoilage and decomposition of many food types is delayed by UV treatment. While the killing of bacteria and mold on food is a primary mechanism, UV also often stimulates various antioxidants in produce. (This not only adds resistance to spoilage, but sometimes increases the nutritional value of the food itself.) Shelf-life and appearance are often enhanced. And if the lifetime is extended, food can travel farther from where it is grown to find new markets.
Food disinfection tunnel with conveyor belt. Courtesy JenAct Limited.
Food-processing UV equipment includes conveyor-belt systems that sweep food into an enclosed Near UV-C irradiated area or “tunnel” that both concentrates UV while protecting workers from skin and eye exposure.
Far UV-C Safety
Numerous scientific studies have shown that Far UV-C, generally in the range of 200 to 230 nm, causes relatively no harm to human skin and eyes.
- A 2018 study from Hirosaki University in Japan found that far UV-C in the range of 222 nm did not induce skin damage on lab mice. The rays were able to penetrate small, thin cell bacteria, but not much larger mammalian skin cells. (The research also discussed a previous study showing no harm from 207 nm light.). Far UV-C does not penetrate skin past the outer (dead-cell) layer, so it does not reach or harm the basal levels which might induce skin cancer over time. This was in contrast to harm displayed by conventional 254 nm UV-C light. (Human skin cells are also larger than bacteria.)
- In 2021, another Japanese study from Shimane University showed that lab animals exposed to extremely large doses of Far UV-C experienced only mild effects at the outer tear layer of their eyes. The rays were not strong enough to penetrate further and cause major damage to vision. This greatly contrasted to damage caused by near UV-C. The “lowest observed adverse effect level” benchmark for Far UV-C at 222 nm was 250 times higher than for conventional Near UV-C (254 nm) rays. This health benchmark was 750 times higher for Far UV-C at the 207 nm level. And even these minor eye irritations were absent after 12 hours due to the normal process of cell restoration.
- A 2017 study from the Columbia University Medical Center found that Far UV-C light killed bacteria efficiently without the harm to skin caused by conventional Near UV-C lamps.
Above is a chart from this report comparing an indicator of premutagenic skin lesions (CPDs) between 222 nm UV-C and conventional 254 nm UV-C. Far UV-C exhibits almost no measurable harm. (Fluence refers to light intensity. Keratinocytes are protein-producing skin cells.)
This is despite near UV-C being almost as effective at deactivating bacteria. Above is a comparison chart of effectiveness at various intensities. The scale at the right is a more common numerical scale.
- A 2018 study from the Columbia University Medical Center proved that far-UVC (222 nm) light inactivated >95% of aerosolized flu virus despite using very low doses of it.
- A 2020 study conducted by some of the same Columbia researchers in the previously cited study estimated a 90% inactivation rate of coronaviruses from Far UV-C at the current (relatively low) regulatory limit of exposure in 8 minutes, and a 99.9% inactivation in only 25 minutes.
- Even the danger of skin cancer from Near UV-C is greatly reduced compared to the oft-times common exposure from UV-B sunburn. Since Near UV-C is less penetrating to the basal layer of skin, 260 nm rays are about 1% as carcinogenic as 300 nm rays.
- Recent information on Far UV-C safety has led to the recommendation that safety thresholds of exposure for UV-C be revised to be much less conservative: at the 222 nm level to about 7 times higher for eyes and 21 times higher for skin; at the 207 nm level to about 32 times higher for eyes and 74 times higher for skin.
UV-C Disinfectant Products
Courtesy Pixabay, Yan Krukov
Publishing a specific guide for this article that includes several thousand UV-C products on the market would be unwieldy for most readers to navigate. Listing large commercial equipment would not be relevant to most readers, as they do not own their own hospital or municipal water treatment plant. And listing every home product available would also be confusing, as products vary widely in function, price, and quality.
Smaller air and surface UV-C disinfection products such as table-lamp disinfection units and wands can often be found in hardware stores and online shopping venues. Many are available for under $100.
Some large commercial UV equipment, used to disinfect food, healthcare facilities, offices, public transportation facilities and vehicles, schools, swimming pools, and water and wastewater treatment plants, can be found in the International Ultraviolet Association’s Buyer’s Guide, accessed at this link. Not all manufacturers are members of the organization and listed in the Guide, but it is a place to start. Professional products can cost thousands of dollars. Some UV-disinfection robots cost over $100,000.
The Environmental Directory has identified companies and resources for UV products in a few niche categories below to assist readers.
Far UV-C Products
The Directory has listed some of the suppliers of Far UV-C products (not considered harmful to skin and eyes) that are currently available at this time. It is highly likely that the number and variety of these products will grow as the technology develops further.
|Far UV Technologies||Krypton Series||faruv.com||Upper-Air Mounted on Lamp Base; Ceiling Mount; Transportation; Portable Surface (Commercial)|
|FarUV Innovations||Quanta Series||faruvinnovations.com||Ceiling Mount; Desk/Table Pods; Hand Sterilizer|
|Larson Electronics||larsonelectronics.com||Ceiling, Wall, & Floor Mount; Recessed Cans & Squares; Track Lights; Door Barriers; Wall Sconce for Air and Surfaces; Desktop Disinfectant; Hand-Held; Cabinets; Portable Industrial; Vehicles; Wristband Mounted|
|Puro Lighting||Protect 222||purolighting.com||Ceiling & Wall Mount; Lighting Fixture Mount|
|QNICEUVC||qniceuvc.com||Desk & Table Lamp; Ceiling & Wall Mount; Transportation; Door Barriers; Hand Sterilizer|
|rzero||Vive||rzero.com||Portable Air and Surface; Ceiling Mount|
|Ushio USA||Far Field Care 222||ushio.com||Recessed Can|
Home UV Air Filters
There are literally thousands of home air cleaners that have been approved for sale in the U.S. They vary greatly in their effectiveness, cost, and energy efficiency. Some units include both an air filtration system and a UV light source for disinfection.
There are 3 databases that allow customers to find these products; they all have search functions that allow the location of UV-assisted models. (By typing in “UV,” they will locate the abbreviation in a product’s name or model number.)
To remind readers, UV in small air filters are not as effective as upper-air systems. They are more suitable to disinfect the air in small enclosed spaces. And it will increase effectiveness of the UV disinfection process if the air cleaners are run at their lowest speed. This will allow the air more “residence” time in the unit for treatment.
The air-cleaning effectiveness of this appliance is rated by a Clean Air Delivery Rate (CADR) standard for removing particulates in each of 3 categories:
Smoke CADR: 10 to 600
Dust CADR: 10 to 600
Pollen CADR: 25 to 450
Association of Home Appliance Manufacturers
The AHAM database allows a comprehensive search by: Room Size; Brand, EnergyStar® rating; and CADR effectiveness. As of June 10, 2022, almost 800 models were listed; 14 had “UV” in the name or model number. (Note: the “UV” search needs to be conducted in the download PDF version of this database.)
The database is at this link.
Since 2010, CARB has required all units sold to customers in the state of California be certified to ensure electrical safety and extremely small levels of ozone emissions. As of June 10, 2022, over 6,100 models had been approved; 259 have “UV” in the name or model number.
The database is at this link.
The STAR database allows a comprehensive search by: Room Size; Brand, EnergyStar® rating; CADR effectiveness; Technology Type; and Electric Consumption (to measure energy efficiency). As of June 10, 2022, over 400 models were listed; 17 had “UV” in the name or model number.
The database is at this link.
The National Sanitation Foundation
NSF certifies water filtration systems for homes and buildings based on structural integrity, material safety, and efficiency of removal various pollutants such of bacteria and viruses, the toxic heavy metal lead, minerals that taint taste, chlorine, and organic pollutants such as VOCs, pesticide, and drug residues that have entered the water supply.
Different types of systems (UV, reverse osmosis, carbon filtration) have different pollutant removal qualities. However, each product must be tested by NSF to clear approval for its pollutant removal claims. UV filtration is sometimes used to augment other types of filters.
(A text search for the term “UV” will locate the abbreviation in a product’s name or model number.)
As of June 10, 2022, there were 568 UV units listed. Almost all of them were in the categories “Under-the-sink or plumbed-in systems” and “UV microbiological treatment systems.”
The database is at this link.
 Gharpure R, Hunter CM, Schnall AH, et al., “Knowledge and Practices Regarding Safe Household Cleaning and Disinfection for COVID-19 Prevention — United States, May 2020,” Atlanta, GA: Center for Disease Control and Prevention, MMWR Morbidity Mortality Weekly Report, Volume 69, June 2, pp. 705–709. Online at http://dx.doi.org/10.15585/mmwr.mm6923e2
 Johnson, Carol and Cincy A. Gaas, “Vinegar: Medicinal Uses and Antiglycemic Effect,” Medscape General Medicine, May 30, 2006, Online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1785201/
 Mas, A, et al., “Vinegar,” Encyclopedia of Food and Health, 2016, pp. 418-423. Online at https://doi.org/10.1016/B978-0-12-384947-2.00726-1
 Cortesia, Claudia, et al., “Acetic Acid, the Active Component of Vinegar, Is an Effective Tuberculocidal Disinfectant,” mBio, Volume 5, Issue 2, March/April 2014. Online at https://journals.asm.org/doi/10.1128/mBio.00013-14
 Goodyear, N., “The effectiveness of three home products in cleaning and disinfection of Staphylococcus aureus and Escherichia coli on home environmental surfaces,” Journal of Applied Biology, Volume 119, August 4, 2015, pp. 1245—1252. Online at https://sfamjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/jam.12935
 Zinn, Marc-Kevin and Dirk Bockmühl, “Did granny know best? Evaluating the antibacterial, antifungal and antiviral efficacy of acetic acid for home care procedures,” BMC Microbiology, August 26, 2020, Article 265. Online at https://bmcmicrobiol.biomedcentral.com/articles/10.1186/s12866-020-01948-8
 Pseudomonas aeruginosa, found in water and soil, can cause infections in the blood, lungs (pneumonia), or other parts of the body after surgery. In 2017, multidrug-resistant Pseudomonas aeruginosa caused an estimated 32,600 infections among hospitalized patients and 2,700 estimated deaths in the United States.
Escherichia coli is a generic class of bacteria found in human and animal intestinal tracts. Most are harmless, though some kinds of E. coli can cause diarrhea, urinary tract infections, respiratory illness and pneumonia, and other illnesses. Dangerous varieties are often transmitted through food and water contamination. Still other kinds of E. coli, even if they are not dangerous, are used as markers for water contamination.
Staphylococcus aureus is a germ carried in the noses of about 30% of people. Though often innocuous, it can cause severe diseases: blood poisoning or sepsis; pneumonia; endocarditis or infection of the heat values; and osteomyelitis or bone infection. Harmful outcomes are often associated with medical procedures in health care facilities and injected drug use.
Methicillin-resistant Staphylococcus aureus (MRSA) is a staph germ that has genetically evolved resistance to common antibiotics due to rampant overuse of them by various industries. In the worst cases, it can infect surgical wounds, the bloodstream, the lungs, or the urinary tract, or cause serious skin infections, which (in rare cases) are realized as “flesh-eating” bacteria. In 2017, about 80,000 MRSA infections were recorded in the U.S., with about 11,000 resulting in death.
Aspergillus brasiliensis is a strain of aspergillus mold that, in some circumstances, can cause allergies, lung and sinus infections, and can spread to hurt other parts of the body. While most people are not afflicted by it, people in weakened states, such as patients with wounds and recent surgery, and the immue-compromised, are more likely to be affected. Nearly 15,000 aspergillosis-associated hospitalizations occurred in the United States in 2014, at an estimated cost of $1.2 billion.
Listeria monocytogenes is one of the causes of common food poisoning. Milder symptoms include a fever, muscle aches, vomiting, and diarrhea. More severe symptoms include headaches, loss of balance, and convulsions. It can actually be fatal, particularly in the young, the elderly, and the immune-compromised.
Klebsiella pneumoniae bacteria can cause pneumonia, blood, wound, and surgical infections, and meningitis to people in a weakened state in health care facilities.
Enterococcus hirae is part of a genus of bacteria that live in the human intestinal tract. The organisms are usually not harmful, but like E. coli, serve as markers for more dangerous organisms that come with fecal contamination of water.
The Modified Vaccinia (virus) Ankara (MVA) is a vector system to develop vaccines against infectious diseases.
 Per online Log Reduction Calculator, Online at https://www.omnicalculator.com/biology/log-reduction
 Greatorex, Jane, et al., “Effectiveness of Common Household Cleaning Agents in Reducing the Viability of Human Influenza A/H1N1,” PLoS ONE, Volume 5, Issue 2, February 2010. Online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2813869/#:~:text=Our%20data%20suggest%20that%201,0.01%25)%20inactivated%20the%20virus.
 Goodyear, N. op. cit., Endnote 5.
 Entani, Etsuzo, et al., “Antibacterial Action of Vinegar against Food-Borne Pathogenic Bacteria Including Escherichia coli 0157:H7,” Journal of Food Protection, Volume 61, No.8, 1998, Pages 953-959. Online at https://pubmed.ncbi.nlm.nih.gov/9713753/
 Cortesia, Claudia op. cit., Endnote 4.
 Yagnik, Darshna et al., “Antibacterial apple cider vinegar eradicates methicillin resistant Staphylococcus aureus and resistant Escherichia coli,” Scientific Reports, Volume 11:1854, 2021. Online at https://doi.org/10.1038/s41598-020-78407-x
 Medina, Eduardo, et al., “Antimicrobial Activity of Olive Oil, Vinegar, and Various Beverages against Foodborne Pathogens,” Journal of Food Protection, Volume 70, Number 5, 2007, pp. 1194–1199. Online at this link.
 Park, Kyung-Min , “Antimicrobial Effect of Acetic Acid, Sodium Hypochlorite, and Thermal Treatments against Psychrotolerant Bacillus cereus Group Isolated from Lettuce (Lactuca sativa L.), “ Foods, Volume 10 (2165), October 2021. Online at https://doi.org/10.3390/foods10092165
 Halstead, Fenella, et al., “The Antibacterial Activity of Acetic Acid against Biofilm-Producing Pathogens of Relevance to Burns Patients,” PLoS ONE, Volume 10 (1371). September 9, 2015. Online at https://pubmed.ncbi.nlm.nih.gov/26352256/
 Rutala, William A., et al., “Antimicrobial Activity of Home Disinfectants and Natural Products Against Potential Human Pathogens,” Infection Control and Hospital Epidemiology, Volume 21, Number 1, January 2000, pp. 33-38. Online at https://pubmed.ncbi.nlm.nih.gov/10656352/
 Much of the historical information in this article is documented in two sources:
Hockberger, Philip, History of Ultraviolet Photobiology, Chicago, IL: Northwestern University, 2002. Online at http://photobiology.info/Hockberger.html
Reed, Nicholas, “The History of Ultraviolet Germicidal Irradiation for Air Disinfection,” Public Health Reports, January-February 2010, Volume 125 (1), pp. 15-27. Online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2789813/pdf/phr125000015.pdf
 Cleaves, Margaret A., Light Therapy, New York, NY: Redman Company, 1904, p. 592. Online at https://www.google.com/books/edition/_/s5A0AQAAMAAJ?hl=en&gbpv=1&pg=PA592&dq=Festner+scarlet+fever+red+light
 Gøtzsche, P.C., “Niels Finsen’s treatment for lupus vulgaris,” Journal of the Royal Society of Medicine, Volume 104, January 1, 2011, pp. 41-2.
Online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3014565/?report=classic
 Sehulster, Lynne and Raymond Y.W. Chinn, “Guidelines for Environmental Infection Control in Health-Care Facilities,” Background C. Air, Atlanta, GA: U.S. Center for Disease Control and Prevention, 2003. Online at https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/air.html
 U.S. Federal Emergency Management Agency, Reference Manual to Mitigate Potential Terrorist Attacks Against Buildings, December 2003, Chapter 5, pp. 5-19, 5-20. Online at https://www.fema.gov/sites/default/files/2020-08/fema426_0.pdf
 Applied Research-west, Inc., 2021 WQA Consumer Opinion Study Summary Report, March 2021.
 Darré, M.; Vicente, A.R.; Cisneros-Zevallos, L.; Artés-Hernández, F. Postharvest Ultraviolet Radiation in Fruit and Vegetables: Applications and Factors Modulating Its Efficacy on Bioactive Compounds and Microbial Growth. Foods2022,11,653. https://doi.org/ 10.3390/foods11050653
 Narita K., Asano K., Morimoto Y., Igarashi T., Nakane A., “Chronic irradiation with 222- nm UVC light induces neither DNA damage nor epidermal lesions in mouse skin, even at high doses,” PLoS ONE, Volume 13, Issue 7, July 25, 2018. Online at https://pubmed.ncbi.nlm.nih.gov/30044862/
 Sachiko Kaidzu, Kazunobu Sugihara, Masahiro Sasaki, Aiko Nishiaki, Hiroyuki Ohashi, Tatsushi Igarashi2 and Masaki Tanito, “Re-Evaluation of Rat Corneal Damage by Short-Wavelength UV Revealed Extremely Less Hazardous Property of Far-UV-C,” Photochemistry and Photobiology, March 22, 2021, Volume 97, pp. 505–516. Online at https://pubmed.ncbi.nlm.nih.gov/33749837/
 Buonanno, Manuela, Brian Ponnaiya, David Welch, Milda Stanislauskas, Gerhard Randers-Pehrson, Lubomir Smilenov, Franklin D. Lowy, David M. Owens, and David J. Brenner, “Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light,” Radiation Research, April 2017, Volume 18, Issue 4, pp. 483–491. Online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5552051/
 Welch, David, Manuela Buonanno, Veljko Grilj, Igor Shuryak, Connor Crickmore, Alan W. Bigelow, Gerhard Randers-Pehrson, Gary W. Johnson & David J. Brenner, “Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases,” Scientific Reports, February 9, 2018, 8: Article 2752. Online at https://www.nature.com/articles/s41598-018-21058-w
 Buonanno, Manuela, David Welch, Igor Shuryak & David J. Brenner, “Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses,” Nature Portfolio, 2020, 10:10285. Online at https://pubmed.ncbi.nlm.nih.gov/32581288/
 David H. Sliney and Bruce E. Stuck, “A Need to Revise Human Exposure Limits for Ultraviolet UV-C Radiation,” Photochemistry and Photobiology, Vol. 97, 2021, pp. 485–492. Online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8252557/