The Medical Minute: Sun protection

July 14, 2010

By John J. Messmer

Here we are in the middle of the sun and fun season, where activities might include picnics, visits to the beach, outdoor sports, gardening and more. Summer sun is good for plants and the extra light is helpful for people with seasonal affective disorder, but be careful -- we can get too much of a good thing.

In addition to the light we can see, sunlight includes the ultraviolet (UV) spectrum that we cannot see. Even though UV light is not visible to us, its effects are. The UV spectrum is divided into three parts, each with different biologic effects: UVA, UVB and UVC. All three parts of the UV spectrum can cause harm, but UVC, the most dangerous part, and part of the UVB are blocked by the ozone layer of our atmosphere.

A little UV exposure is beneficial, but you don’t need much. UV light helps us produce vitamin D that benefits our bones and immune systems. Exposing the arms and face for 5 to 10 minutes two to three times per week during spring and summer makes plenty of vitamin D for white skinned people. Darker skin requires just a little more exposure. Too much exposure breaks down the vitamin D that has been formed. But we really don’t need the sun for vitamin D -- we can get plenty of vitamin D in food, such as vitamin D milk and in fish or as a supplement. Additionally, the sun is not intense enough in the northern United States from October to April to be a reliable vitamin D source so food or supplementation is better.

UV light from the sun increases the development of one type of cataract. Too much sun makes us look older -- a process called “photoaging.” The UV light breaks down the supporting structures so skin wrinkles and sags. The upper skin layers react to sun exposure by getting rough and flaky with dilated blood vessels. The lighter one’s pigmentation, the more this happens. Thus, we have a choice if we have light skin color: do we want to be fashionable with a tan now or look younger than our age later?

Photoaging is harmless, but cancer is not. UV light is the primary cause of skin cancer. Melanoma in particular, the most dangerous skin cancer, is occurring at greater frequency and in younger people than ever before, most likely due to sun exposure and indoor tanning. Tanning may reduce the chance of sunburn slightly, but it greatly increases the risk of skin cancer. UV light causes cancer by damaging the cell’s DNA, but it also impairs the skin’s immune system, preventing it from attacking newly developed cancers. The truth is, there is no such thing as a healthy tan.

Fortunately, there are ways to reduce your exposure to UV light. Sunblock works if used correctly. It must be applied liberally to exposed dry skin and reapplied when the skin has been wet from swimming or sweating. Even water-resistant sun block is not waterproof.

The sun protective factor, or SPF, tells us how much protection the sun block provides. The number predicts how much longer a person using it can stay in the sun before burning compared to using nothing. But sunburn is only half the reason to use sunblock. To slow photoaging and reduce cancer risk, blocking as much UV light as possible should be the goal.

An SPF 15 blocks about 93 percent of UVB and SPF 45 blocks about 98 percent. Generally, most people should consider using at least an spf 30 for exposures between 10 a.m. and 2 p.m. unless they have very sensitive skin. The spf pertains only to UVB. Most sunblocks are now “broad spectrum” meaning they block both UVA and UVB.

Sunglasses can help keep UV light out of the eyes. Be sure that the glasses are marked 100 percent UVA and UVB protection or similar words. Not all sunglasses have this protection. Not having UV protections is worse than no sunglasses since cutting down visible light allows the pupils to enlarge letting in more UV. Also, sunlight will pass around the sunglasses so a wide-brimmed hat helps keep it off your eyes and face and protects the scalp, particularly in those whose hair is thinning.

Covering up as much as is comfortable works even better than sunblock, and sitting in shade helps, too. It’s a little safer before 10 a.m. and in the evening and it’s usually cooler, too, so try to plan your yard work and other activities for these times, if possible. At the pool and the beach, get under a tree or umbrella, cover up as much as is reasonable and use and reuse sunblock generously.

A special note for babies and children: Younger skin is even more sensitive, and damage done now will affect them as adults. Each sunburn increases the risk of melanoma, and excess sun exposure as a child makes the skin age quickly.

Summer sun can be fun and safe by taking precautions to keep your skin young and cancer-free.

John J. Messmer, M.D., is an associate professor of Family and Community Medicine and associate vice chair for Inpatient Medicine, Penn State Hershey Medical Group, Palmyra.

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Last Updated July 27, 2010