How Does the Sun Cause Sunburn?

The Science

Practically everyone, at one time or another, has experienced the discomfort and itchiness that accompanies sunburn. Your skin turns an unattractive--and painful--shade of red, and when the pain and redness finally go away, your skin starts peeling off! But what causes all this? You can blame your burning pain on the ultraviolet (UV) radiation in the sun's rays. There are three different types of UV rays: UVA, UVB and UVC. Each type of UV ray causes premature aging and destroys vitamin A in the skin. However, UVB rays are the ones responsible for that red hot pain. Because these these rays only reach the top layer of the skin (the only visible layer), they cause cosmetic damage to the skin--otherwise known as sunburn.

Ultraviolet Rays

A sunburn is literally an ultraviolet burn to the skin. UVC rays are the most dangerous type of ultraviolet radiation, but fortunately, these rays are absorbed by the earth's ozone layer and therefore, do not reach us. However, this is not the case for UVA and UVB rays. Although UVA rays are more abundant than UVB rays, they do not cause sunburn. They actually penetrate all the way to the base layer of the skin and cause no visible damage to your skin.

But Why Do I Burn?

UVB rays penetrate only the top layer of your skin, and your body's natural reaction is to protect your skin from damage. To do this, your skin needs a certain amount of melanin--its protective pigment. The amount of melanin in your skin is based on your natural skin color--darker skin indicates higher amounts of melanin. Because the amount of melanin in your skin is determined by your genetic makeup, when your skin is overexposed to UVB rays, your body does not have enough melanin to adequately protect itself. The sun's rays literally damage your skin cells, turning the top layer of your skin red, hot and sun-bruised. Typically, the effects of sunburn are visible about two to six hours after exposure. The damaged skin remains red for three to five days afterward, then rids itself of those damaged cells by peeling.

Resources

• Protect yourself from sunburn