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The ABC's of UV Light

Jul 13, 2020

Suntans and COVID

July, appropriately, is UV awareness month. It is now the height of summer and most of us will be spending more time outdoors.  So time to be mindful of sun protection.

Our main source of UV light (a form of electromagnetic radiation) is from the sun. There are 3 types of ultraviolet radiation: A,B,C with a range of range of wavelengths between 10-400 nm( just below the visible spectrum). All UVA radiation penetrates the ozone layer, some UVB passes through and no UVC C can get through.  There are beneficial effects of ultraviolet radiation (vitamin D production for example) but also some health risks.

UVB represents only 5% of the UV radiation that reaches the earths surface but it is the most biologically active and potentially damaging - responsible for sunburn, inflammation, cataracts and photocarcinogenesis (melanoma specifically). UVA is not harmless as it can also cause sunburn, carcinogenesis and skin aging. It also can penetrate cloud cover and glass. Most UVC radiation is dangerous to humans but it does not penetrate the ozone layer.  Skin protection by use of appropriate clothing and sunscreens is important to prevent these adverse effects. The American Academy of Dermatology recommend products that have broad spectrum coverage (for both UVA and B) and an SPF factor of 30 or above and are water and sweat resistant. The product should be generously applied:

approximately 1 teaspoon to the face and neck area, a total of 2 teaspoons to the front and back ,1 teaspoon to each arm, and 2 teaspoons to each leg. They should be reapplied approximately every 2 hours and after swimming even if labeled water resistant.

Since many of our patients are taking medication occasionally or regularly it is important to note that there are several medications that cause “photosensitivity” (an increase likelihood of sunburn in a shorter period of time). These medications include:

 Lasix (furosemide), Hydrodiuril (hydrochlorothiazide)

Cipro (ciprofloxacin, Levaquin (levofloxacin), Vibramycin (doxycycline), Bactrim (trimethoprim/sulfamethoxazole)

Motrin (ibuprofen), Aleve (naproxen), Celebrex (celecoxib

Benadryl (diphenhydramine)

Phenergan (promethazine

Birth control pills

Accutane (isotretinoin), Retin-A (tretinoin)

Shorter time in the sun, decrease skin exposure and more frequent application of sunscreens is recommended if you are taking any of these medications


So what’s the association of COVID with ultraviolet light?

UVC light is part of the shorter spectrum UV wavelength.  It has been known for a long time to be germicidal for viruses and bacteria. Hospitals are using this light as a means of sterilization of large spaces and the MTA is using it at night when the subways are shut down. The common sources produce UVC at 254 nm which can penetrate the keratin layer and cause damage to skin and eyes. This therefore limits its use. Far-UVC light (222nm) wavelength does not penetrate keratin and is harmless to humans. It has the potential of being used as a sterilization method for office buildings and other large inhabited area. This would obviously be of great utility as the world returns to more normal activities.