November 17, 2006

Sun protection in the winter equally important as summer

By Donna Lee, M.D.
Special to the Times

This article contains general medical information only; it is not a substitute for personal visits with your own physician. Since every patient’s situation is unique, please contact your personal physician for specific advice regarding your health.

Most people understand the importance of sun protection in the summer and are fairly consistent about using their sunscreen every day in the hot weather.

But many people do not realize they also need UV protection in the winter. To understand why, it helps to have some background in the types of UV radiation and different chemicals to block them.

UV radiation can be classified as UVA (wavelength of 320 – 400 nm), UVB (290 – 320 nm), and UVC (100 – 290 nm). Luckily for us, UVC rays are currently completely blocked by the ozone layer, so we will focus on UVA and UVB in this article. Both of these types of rays can pass through the atmosphere and are present even on cloudy and foggy days. And both can cause skin cancer. A simple way of categorizing them is to think of UVA as the “aging” rays, the ones that pass through the epidermis (the top layer of skin) and into the dermis (the middle layer) to produce wrinkles, sagging, and brown spots. UVB rays tend to be the “burning” rays, the ones mostly absorbed by the epidermis to cause the redness and heat we think of as a sunburn.

The other major difference between UVA and UVB is that UVB rays do not penetrate well through windows and clothing, but UVA rays do. Even people who are indoors all day are exposed to the “photo-aging” rays. In fact, any time you can read a page comfortably without needing to turn on an artificial light, you are getting UVA exposure.

Most of the sunscreens available are very good at blocking UVB, but not as proficient at blocking UVA. In fact, the SPF number that so many people focus on only tells us about UVB blockage, and does not indicate whether a sunscreen offers any protection against UVA rays. This is because the SPF number is a measurement of how much longer a person can stay in the sun before he/she burns (UVB).

The best way to look for coverage against both UVA and UVB is to look for zinc oxide, at least 3.5 percent, as a main ingredient. There are other good UVA blockers containing combinations of titanium dioxide, avobenzone (Parsol), oxybenzone, octinoxate, octocrylene, and mexoryl. These ingredients separately only cover a portion of the UVA spectrum, but when combined into one product, can be effective at covering the whole spectrum.

If you do not want to remember long ingredient lists, you can look for the skin cancer foundation’s seal of approval. Having the seal means a sunscreen manufacturer has paid the organization a fee to have its product tested to prove it provides broad-spectrum protection and can prevent skin cancer. But many manufacturers of good products have opted not to pay this fee, so absence of the seal does not necessarily mean the sunscreen in inferior.

There is some controversy over the concept of physical blocks versus chemical screens. Zinc oxide is a physical block, which means that it sits on the surface of the skin rather than becoming absorbed into the skin. It acts as a mirror, reflecting away UV rays.

Ingredients such as avobenzone and mexoryl are chemical screens, which mean that they absorb the UV energy and convert it into lower (and non-cancer causing) types of energy. Proponents of zinc believe that it is better to stop the UV rays before they reach the skin at all, but proponents of chemical screens believe the coating of zinc prevents the skin from “breathing” and traps in heat. To counter this, there are formulations of physical blocks that include iron oxides, which block infrared rays (the rays most responsible for generating heat). In the chemical screen camp, there is some research indicating that avobenzone is better than zinc at protecting the skin’s immune system, which is the first line of defense against early skin cancer cells. In my view, there is a role for both physical blocks and chemical screens; I suggest to patients that they wear both whenever they can.

Many people believe the mantra of reapplying sunscreen every two hours is propaganda put out by manufacturers to get us to buy more, but reapplication really is the best way to make sure we are protected. Many ingredients, especially avobenzone, start to break down as soon as they are exposed to the sun. Luckily, newer products such as powder sun block brushes make it easy for people to reapply sun block without removing and reapplying makeup.
Protect yourself from the sun, even in the winter!

Dr. Lee is board certified in internal medicine and has recently moved her practice to Evergreen. She is also the medical director of Clarity Medical Spa. She has a special interest in cosmetic dermatology and patient education. Contact her office at (408) 270-3877 or visit www.claritymedicalspa.com.