Find a Trail

Here Comes the Sunburn

Hiking sunburn

By Dr. Gus Benner

Every season is the right time to protect yourself from the sun. Knowing a bit about what's going with

Ultraviolet radiation (UVR) comes in three flavors: UVC, UVB, and UVA. UVC is the most damaging, but almost none of this reaches the earth, being blocked out by our atmosphere; ozone helps here.

Here are some facts about UVB and UVA:

  • UVB is the traditional radiation of concern, and causes reddening of the skin (erythema) and the familiar sunburn. As bad as the effect of UVB can be, it is relatively superficial, penetrating only a few microns into the skin. UVB is much more intense in midday, say between 10 a.m. and 3 p.m., and tends to be filtered out before and after, as the sunlight passes through more atmosphere to reach us.
  • UVA, which penetrates deeper into the skin, is less able to produce a burn, but can over time produce a tan, and is used in tanning parlors. It is responsible for some of the aging changes in the skin, and can combine with some drugs (e.g. tetracyclines) to produce photosensitivity reactions. All sunlight contains UVA, all day.

    UVR can pass through clouds that are blocking visible light, and we've all probably gotten some erythema or sunburn on days we never saw the sun. Particularly in reference to sunglasses, it is possible for a dark glass to allow significant UVR through, and for a clear glass to totally block UVR.

    (The worst sunburn we can get is of the cornea: It is very painful and can effectively temporarily blind you. The cheapest glasses we can get, either glass or plastic, do block some UVR (60-75%), but a UV protective coating is easy to add, and most good dark glasses do specify 100% UV blockage. There's hardly an excuse not to use such glasses in high-exposure situations.)

    The bad news is this: UVR of any kind is bad for us. It burns. It alters DNA, causes mutagenesis, and increases the risk of skin cancer. A gradually acquired tan can reduce the chance of a burn, but you can't get it without gradually damaging the DNA. If a cosmetic tan is your goal, there are good tanning lotions that stain the skin without any exposure to sunlight, and they last for several days. They do not, however, confer protection from burning and DNA damage.

    How can we prevent UVR damage?

    The simplest way is to keep out of the sun, especially midday. If you are lounging at a beach resort, taking a noon-time nap in the shade might be an option, but we usually want to be out and about. So the next line of defense is clothing. This is fine, but recognize that it is not 100%. A white cotton T-shirt has an SPF (sun protection factor) of about 6 (3 if it's wet), so you can get a burn through it. There are specialty lines of clothing that have much better UVR blockage in a lightweight thin garment. A wide-brim hat is important but reflected light from snow, sand, or water will still get to your face.

    Sunscreens are our major (skin) defense. Years ago we were primarily concerned with UVB, the easy advice was to get PABA, a very good UVB blocker. How easy it is to have better judgment in retrospect. PABA does not block UVA, and has a relatively high incidence of sensitivity reactions, so now a major advertizing claim of products is that they are "PABA free".

    Current sunscreens block UVR either chemically or physically.

    The physical blockers, zinc oxide and titanium dioxide, just layer on your skin and block out sunlight, with very good blockage of UVA and UVB. They used to be cosmetically less attrractive, as they were a visible white paste (you remember zinc oxide on lifeguards at the pool?). Now the titanium dioxide is micronized, and it rubs in invisibly.

    There are many chemical blockers, and all of them are good UVB blockers. Common ingredients seen are cinnamates or salicylates. The ones that have UVA blockage are the benzones (oxy or dioxy), avobenzone (Parsol 1789), octocrylene, and menthyl anthanilate.
    We measure effectiveness by the SPF (sun protection factor), which measures how much longer the sunscreen will allow us to stay in the sun before getting erythema. An SPF of 6 means we can stay out 6 times longer than we could without a sunscreen before getting red. Under ideal conditions, using an SPF beyond 15 was not thought to confer much additional benefit. However, conditions in the wild are not always ideal, and we may not apply the exact thickness that givs the labeled SPF, so going for a higher SPF (e.g. 30) is probably worthwhile.

    Remember, the SPF only measures UVB blockage. You need to read the fine print to see if it has UVA blockage.

    "Water resistant" formulas maintain protection after 40 minutes in the water; "water proof" formulas work up to 80 minutes. "Sweat resistant" means it can withstand 30 minutes of sweating.

    You also need the right-sized container. A knapsacker needs a different container than someone rafting 18 days on the Colorado River. How solid is the container and its closure? All of these are important matters of personal preference. I bet many of you have shared my grief at finding sunscreen broken out all over your waist pack.
  • Dr. Gus Benner is the Sierra Club Outings Committee's Medical Adviser. His articles ioriginally appeared in the Inside Outings newsletter. Requests to use or copy this material should be addressed to Dr. Benner c/o Inside Outings.