DEAR DR. DONOHUE: I have two daughters at home from college for the summer. Both are excellent swimmers and have been swimming since they were 7 years old. They have jobs as lifeguards. This is their second summer lifeguarding. I wonder what kind of danger they put themselves in from all this sun exposure. What do you say? - C.F.
We can't live without the sun. One of its benefits is the generation of vitamin D in the skin. However, it takes a relatively brief exposure to summer sun to accomplish the production of this vitamin. Some say 15 minutes in the noonday sun three times a week is enough. Others claim daily exposure of two to eight minutes is sufficient.
The downside of sun exposure is the damage to the DNA of skin cells by the sun's ultraviolet rays, a prelude to cancer changes. Ultraviolet B rays are the rays responsible for sunburns and are the more dangerous in promoting cancer changes. Ultraviolet A rays promote tanning. These rays are the ones that age skin, causing it to wrinkle. People need to protect the skin from both.
Outdoor lifeguards should sit under an umbrella. They need to generously apply sunscreen to their skin. The best sunscreen affords protection against both UV-A and UV-B rays. They have to reapply the sunscreen every two hours, more frequently if they're sweating. They also need to reapply it after being in the water. The sunscreen should have an SPF (sun protection factor) of 15 to 30.
Even on cloudy days, they have to cover their skin with sunscreen. Up to 80 percent of the sun's ultraviolet rays penetrate through the clouds.
If your daughters are serious about skin protection, they can hold down their lifeguard jobs this and next summer, too.
DR. PAUL DONOHUE is a syndicated columnist with North America Syndicate Inc., P.O. Box 536475, Orlando, FL 32853-6475.