Sunburn means damage to your skin. The pain and discomfort is a sign that damage has occurred. The specific cause is a molecule in the skin called TRPV4, which is also associated with a common hereditary disease that affects the larynx. In the skin—in particular, the outermost epidermal layer of the skin—it responds to the UVB rays in sunlight by triggering a response the brings calcium to the surface of the skin. The calcium, in turn, comes with a chemical called endothelin, which causes pain and itching, but also draws more calcium—and more endothelin. But sunburn does more than suffuse your skin with calcium. Over time, the UV rays that cause sunburn can also lead to skin cancer.
Unfortunately the damage happens early. In fact, according to a recent study, skin cancer risk in middle age or beyond is 80 percent higher in people who had five or more sunburns between ages 15 and 20 —a large increase for what is already the most common form of cancer in the United States. Even study subjects with no family history of skin cancer were more prone to develop it themselves if they had multiple blistering sunburns as adolescents.
The good news is that while early sunburn is a risk, avoiding sunburn even later in life can still provide some measure of protection. People who are especially prone to burning—people with fair skin, people who take certain medications, anyone who drinks while or immediately before going out in the sun—should be especially cautious. That means covering up as much as is possible when going out in the summer. It means wide-brimmed hats and UV-protecting sunglasses. It means staying in the shade, including the portable shade of a parasol for people with a particular tendency to burn.
It also means sunscreen. Experts say that sunscreen doesn't provide complete protection, but it does significantly improve matters. Sunscreen should have a sun protection factor of 30 or higher. A shot-glass-full is enough to cover most adults, though people showing more skin—or people with more skin to show—may need more. Some form of sunburn protection is important even on cloudy days, and even for people who aren't planning to simply soak up rays. It should be applied 15 minutes before going outside and reapplied every two hours. Even waterproof sunscreen could probably stand to be reapplied after it gets wet, especially after a dip in the pool.