It’s happened to most of you. You leave the house for the beach. You forget the sunscreen. Oh well, you think, I won’t stay out in the sun too long. You do stay out in the sun too long, but you’re surprised that you haven’t burned too badly. Still, you feel a heaviness on your skin. That night, you start feeling a burning sensation.
The next morning, you wake up and go into the bathroom. You look in the mirror. George Hamilton is staring back at you. Don’t you hate when that happens?
Despite our association of sunburn and tanning with fun in the sun, sunburn is, to quote U.S. Army dermatologist Col. John R. Cook, nothing more than “an injury to the skin caused by exposure to ultraviolet radiation.” The sun’s ultraviolet rays, ranging in length from 200 to 400 nanometers, invisible to the naked eye, are also responsible for skin cancer. Luckily for us, much of the damaging effects of the sun is filtered by our ozone layer.
Actually, some of us do redden quickly after exposure to the sun, but Samuel T. Selden, a Chesapeake, Virginia, dermatologist, told us that this initial “blush” is primarily due to the heat, with blood going through the skin in an effort to radiate the heat to the outside, reducing the core temperature.
How Your Skin Burns
This initial reaction is not the burn itself. In most cases, the peak burn is reached fifteen to twenty-four hours after exposure. A whole series of events causes the erythema (reddening) of the skin, after a prolonged exposure to the sun:
1. In an attempt to repair damaged cells, vessels widen in order to rush blood to the surface of the skin. As biophysicist Joe Doyle puts it, “The redness we see is not actually the burn, but rather the blood that has come to repair the cells that have burned.” This process, called vasodilation, is prompted by the release of one or more chemicals, such as kinins, setotonins, and histamines.
2. Capillaries break down and slowly leak blood.
3. Exposure to the sun stimulates the skin to manufacture more melanin, the pigment that makes us appear darker (darker-skinned people, in general, can better withstand exposure to the sun, and are more likely to tan than burn).
4. Prostaglandins, fatty acid compounds, are released after cells are damaged by the sun, and play some role in the delay of sunburns, but researchers don’t know yet exactly how this works.
All four of these processes take time and explain the delayed appearance of sunburn. The rate at which an individual will tan is dependent upon the skin type (the amount of melanin already in the skin), the wavelength of the ultraviolet rays, the volume of time in the sun, and the time of day. (If you are tanning at any time other than office hours — 9 A.M. to 5 P.M. — you are unlikely to burn.)
Even after erythema occurs, your body attempts to heal you. Peeling, for example, can be an important defense mechanism, as Dr. Selden explains:
The peeling that takes place as the sunburn progresses is the skin’s effort to thicken up in preparation for further sun exposure. The skin thickens and darkens with each sun exposure, but some individuals, lacking the ability to tan, suffer sunburns with each sun exposure.
One dermatologist, Joseph P. Bark of Lexington, Kentucky, told us that the delayed burning effect is responsible for much of the severe skin damage he sees in his practice. Sunbathers think that if they haven’t burned yet, they can continue sitting in the sun, but there is no way to gauge how much damage one has incurred simply by examining the color or extent of the erythema. To Bark, this is like saying there is no fire when we detect smoke, but no flames. Long before sunburns appear, a doctor can find cell damage by examining samples through a microscope.
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