Is sunlight addictive?

It doesn’t make sense: If sunlight causes cancer, why are human beings so drawn to it, flocking to sunny beaches for vacation time and hoping for sunshine after a rainy spell?

One answer, says David Fisher, chief of dermatology at Harvard-affiliated Massachusetts General Hospital in Boston, may be that humans are literally addicted to sunshine so our skin can make vitamin D. New evidence suggests that we get the same kick out of being in the sun that we get from any addictive substance or behavior. It stimulates the so-called “pleasure center” in the brain and releases a rush of feel-good chemicals like endorphins.

So there may be more than a desire to look good in a tan behind the urge to soak up the sun’s rays. This craving may be a survival mechanism that evolved over thousands of years because humans need vitamin D to survive. Skin makes this crucial vitamin when it is exposed to sunlight. There isn’t much vitamin D in food (except in some of today’s fortified foods) so the human brain rewards us with a rush of pleasure when we seek out the sun and get vitamin D.

Seeking sunshine can be downright dangerous. As Fisher points out, the ultraviolet (UV) radiation from sunshine is “the most ubiquitous and common carcinogen in the world.” Skin cancer is the most preventable form of cancer simply because we know what causes it: sunlight. Yet despite this knowledge, skin cancer is on the rise, increasing faster than any other form of cancer. (You can watch Fisher’s presentation here.)

Avoiding D-ficiency

A simple blood test at your doctor’s office can determine if you are deficient in vitamin D. New guidelines from the Institute of Medicine recommend 600 international units (IU) of vitamin D a day for everyone between the ages of 1 and 70, and 800 IU for those over age 70. Some experts argue that this isn’t enough, and that five to 10 minutes a day outdoors without sunscreen is a reasonable way to get some natural vitamin D. (If you live north of a line connecting San Francisco with St. Louis and Richmond, Virginia, don’t bother doing this between November and March—the amount of ultraviolet light hitting your body won’t be enough to generate vitamin D.)

If you’ll be out longer than five to 10 minutes, cover up. Use sunscreen but understand that the evidence for its long-term protection against skin cancer is “changing rapidly,” says Fisher. Some newer studies show no benefit, some even show elevated risk for people who use sunscreen. More effective protection is a full-brimmed hat and long sleeves and pants. Best choice, says Dr. Fisher, “Stay in the shade.”

For more on caring for your skin, treating age-related skin conditions, and skin rejuvenation, check out the Harvard Health Publication’s Special Health Report: Skin Care and Repair.