Short days and cold temperatures mean that no one is getting significant sun exposure in the winter months, at least not in most of the United States. While it seems safe to stash the sunscreen December through March (or earlier and longer in many northern regions), you should know that winter sunlight can still be damaging.
The earth’s atmosphere provides a lot of protection from powerful UV radiation emitted by the sun. Virtually all UVC rays are deflected or absorbed, and UVB rays can only penetrate the atmosphere at certainangles, meaning that UVB is significantly reduced during winter months. However, UVA rays, the longest in the UV spectrum, can penetrate the earth’s atmosphere—and clouds and glass—all day, every day.
Researchers have known for decades that UVB rays contribute to skin damage. They are the type of radiation that cause sunburns (and frequent sunburns have been shown to increase the risk for certain cancers). Until
recently, though, UVA rays were thought to be skin-safe, causing nothing more than a tan—mild damage that the skin naturally repairs (as evidenced by tan fading). Now, we know that UVA rays are just as damaging as UVB rays, just in different ways.
UVA rays penetrate more deeply than UVB rays, allowing the radiation to affect the lowest layer of the epidermis where keratinocytes are found. Keratinocytes exposed to radiation can mutate, and so begins the development of basal and squamous cell skin cancers.
It is easy to think that without the warmth, the sun’s rays are not strong enough to cause damage, but UVA rays are invisible skin assailants. Fortunately, they affect very little skin because so much of our bodies are covered with warm wear. For the parts that are continually exposed, particularly our faces, you should still apply sun protection.
Because of the abbreviated duration of sun exposure and the natural decrease in UVB rays, less sun protection than that required in the summer is likely sufficient. For instance, using a moisturizer or makeup with SPF may be enough. However, if you are going to be exposed to the sun and other elements (wind and cold), as you would be on a ski excursion or when working outside, a thicker sunscreen and/or sunblock will provide the necessary SPF as well as a barrier against moisture loss that can cause chapping.