Dear Dr. Mirkin: How do you get enough sunlight for your body to make vitamin D without risking skin cancer?

Try to expose a small amount of bare skin to sunlight for a few minutes every day. Wear a shirt and a hat. Put sunscreen on your face, top of the ears, neck, arms and back of the hands. If you are blond or blue eyed, do not form pigment well, or have evidence of sun damaged skin, you should apply sunscreen to your legs also.

• • Non-melanoma skin cancer risk (basal and squamous cell skin cancers) is increased by cumulative sun exposure over a lifetime.
• • Recent data show that a single sunburn may cause a melanoma.
• • It appears that blond and blue-eyed people need less sun exposure to make vitamin D. People with dark skin, or those who become very dark when they tan need far more sun exposure to make vitamin D.
• • Being overweight or past 60 markedly increases your need for vitamin D.
• • Only UVB causes the skin to make vitamin D. UVA does not cause your skin to make vitamin D. Most suncscreens on the market almost completely block UVB. Window glass and clothes also block UVB.
• • Frequent bathing reduces vitamin D. Your sebaceous (oil) glands make vitamin D and secrete it onto your skin; it is then absorbed through your skin. Frequent bathing may wash away vitamin D before it can be absorbed.
• • The following changes in your skin predict skin cancer: first a mottling of pigment with lighter and darker spots, then the appearance of scaly areas. When the scaly areas start to feel rough like sandpaper, the damage is passing from the superficial skin down into the deeper skin and may become cancerous. Check with a dermatologist; these pre-cancers are very easy to treat.