Sunday, August 2, 2020

Sunscreens: are they harmful?

Ah, summer. Beaches, swimming, sailing, outdoor parties, skin cancer.

Wonderful as it is to be outdoors in the sun, there is a potential price to pay. In addition to the visible sunshine and heat we get from the sun, we also get ultraviolet (UV) rays, that are damaging to our skin. There are at least three forms of UV light: A, B and C. All the UVC rays, with the shortest wavelength and which are the most damaging, are absorbed by earth’s ozone layer, as are many of the UVB rays, but most of the UVA and some of the UVB rays reach us. UVB rays on our skin have the valuable function of producing Vitamin D from precursors, so people who avoid all sun may need to take supplements to avoid becoming deficient in D.

UVA and B cause sunburns and are a major risk factor for melanoma and other skin cancers in fair-skinned populations. Some 60,000 people world-wide die of melanoma every year. Not surprisingly, Australia and New Zealand (with large majority Caucasian residents and a lot of outdoor activities) lead the world in melanoma cases per 100,000 people. Next in line are the Nordic countries – presumably because they are the fairest of the fair-skinned peoples. People of African and South Asian descent are much less susceptible to this risk. Melanin is the body’s protection against UV rays, and dark-skinned individuals have more melanin in their skin.

“Suntan lotions” with little UV protection may allow one to get a tan without as much risk of burning, but they offer almost no protection against skin cancer (nor the cosmetic effects of prolonged sun exposure: wrinkles and leathery skin years later).

Enter sunscreens. These come labelled with SPFs (skin protection factors). This number is an estimate of how much longer you can be in the sun without burning; if you would get a burn after 30 minutes in the sun, then a lotion with an SPF of 6 would let you be in the sun for 3 hours before you burned. Most dermatologists recommend using a lotion with an SPF of at least 30 to prevent skin cancer down the road.

One concern is whether habitual use of sunscreens might lead to Vitamin D deficiency, but this does not appear to happen based on recent research.

There has been a lot of press recently about another potential risk. Sunscreens may include organic and inorganic filters. Inorganic filters such as titanium dioxide and zinc oxide physically reflect UV rays away from the skin and are clearly safe. Organic filters, too many to list, absorb UV radiation and are the most widely used because they are colorless. Two trials conducted by the FDA found that “normal” application of sunscreens led to measurable levels of these compounds in the blood of people who used them. The FDA was careful to point out that this was not a reason to stop using them, but simply a call for more research.

If the news stories have you worried, what should you do? I would strongly recommend you not stop protecting your skin. There is no current evidence that the compounds have any harmful effects and any theoretical worries must be balanced against the known carcinogenic effects of the sun’s UV rays.

One obvious step is to use physical barriers: dark umbrellas block most of the UV rays, as does most clothing: denim, nylon and polyester (but less so cotton). If media reports have you worried about sunblock, use zinc or titanium-based products, which the FDA considers totally safe. If you consider those unsightly, use the organic-based products; their “hazards” are conjecture and their benefits proven.

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