DEAR DR. DONOHUE: My two teenage daughters are not having any luck in finding a summer job. We live in a fairly depressed area. They aren’t all that disappointed. They tell me they’ll have time to work on their tans at our nearby lake.

What’s your opinion of tanning? I have heard nothing but bad things about it. My girls say that’s hogwash. Is it? — B.C.

ANSWER: Exposure to the sun’s ultraviolet rays is a prime factor in promoting skin cancer. The cancers appear later in life. Around 1.3 million Americans develop skin cancer each year, and these cancers do not include melanoma, the most dangerous form of skin cancer.

Not only do ultraviolet rays transform skin cells into cancer, they have another effect that might make your girls sit up and take notice. Deep penetration of ultraviolet rays to the lower layer of skin leads to deeply wrinkled skin and gives a person a weather-beaten look. The lower layer of skin contains proteins that support the upper layer.

Everyone who goes outdoors, especially in the summer, and has no intention of working on a tan (just what work is involved?) still needs to protect the skin by wearing sunscreen. Sunscreens are now designated as “broad spectrum” if they protect against both ultraviolet A and ultraviolet B rays. Furthermore, the sunscreen ought to have an SPF (sun protection factor) of 15 or greater.

People who sunbathe must be conscientious about applying sunscreen. A full teaspoon of sunscreen is needed to cover each of these body areas: the face, the ears, neck, front of the trunk, back of the trunk, each arm, the backs of the hands, each upper leg, each lower leg and the top of the feet. Reapply as directions on the product indicate. Stay out of the sun between 10 a.m. and 3 p.m., the time of most intense radiation.

DEAR DR. DONOHUE: I read that all adults are deficient in vitamin D. I know vitamin D comes from sunlight. How does that square with the warning to stay out of the sun? — L.L.

ANSWER: The time needed to convert skin chemicals into vitamin D through the action of sun is not prolonged. I’ll give you two opinions on the length of time. Choose the one that appeals to you.

Six to 18 minutes is enough exposure to sunlight. The lower number is for people who always burn but never tan. The higher number is for people who always tan but never burn.

A more easily followed rule is to limit sun exposure to 15 minutes on the arms and legs two to three times a week. The exposure should take place during the most intense hours of sun radiation, between 10 a.m. and 3 p.m.

In the winter, it’s all but impossible for people in northern climates to achieve their daily recommendation for vitamin D through sun exposure.

DEAR DR. DONOHUE: Please discuss the benefits of water walking. I tread water in the deep end of the pool. My brother water walks in a pool of more shallow water. Which gives the greater benefits? — R.P.

ANSWER: Water walking is an excellent hot-weather exercise. The water keeps people cool. Walking in water requires 12 times the effort that walking on dry land demands. The water buoyancy protects joints. Walking in deep water requires the walker to wear a flotation belt or flotation vest. Walking in chest-high water does not.

You can increase the intensity of walking by walking backward or sideward or raising the knees higher than you usually would do.

Deep-water walking is more strenuous than shallow-water walking.

People who are not used to exercise ought to get a go-ahead from their doctors before they try any kind of exercise.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.

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