How much sun is safe, and does the tanning bed really cause skin cancer?

UV radiation is the primary environmental cause of skin cancer, and that relationship has been established as causal, not merely a statistical association. Between 60 and 70 percent of all melanomas, the deadliest form, are caused by UV exposure, from both the sun and tanning beds. In Western populations, an average of 1 in 50 people will develop melanoma in their lifetime. Basal cell carcinoma, the most common cancer worldwide, shares the same cause, and its incidence continues to rise.

Here is how the mechanism works: UV radiation damages the DNA in skin cells, causes oxidative stress and inflammation. That damage accumulates over the years. It is not a single sunburn that matters, but the total exposure over your lifetime. People who burn regularly as children and young adults carry that damage with them. People with fair skin, red or blond hair, many moles, or a family history of melanoma face additional risk because their genetic makeup allows UV damage to progress to cancer more readily.

What about tanning beds? They emit the same type of UV radiation as the sun, with the same harmful effects. There is no 'safe' variant. People with albinism, who lack the protective skin pigment melanin, show just how dramatically UV damage can play out without protection: in tropical countries this leads to serious skin cancer and sometimes premature death.

Yet the sun also plays a positive role: UVB light converts a substance in the skin into vitamin D3. More than half of the world's population is at risk for vitamin D deficiency, partly due to insufficient sunlight exposure. That deficiency is associated with bone problems such as rickets and osteoporosis, and possibly with a higher risk of certain cancers, autoimmune diseases and cardiovascular disease, although that last link for non-bone conditions has not yet been fully proven. Dark skin, high latitude, old age and sunscreen all reduce the production of vitamin D through the skin.

The practical balance: short, regular sun exposure in the afternoon (face and arms, 10 to 20 minutes on a sunny day, depending on your skin type and the UV index) produces vitamin D without causing significant damage. You should avoid burning under all circumstances. The tanning bed is best avoided as a source of vitamin D: the risk of skin cancer does not outweigh the vitamin D you get from it, especially since supplementation is a safe alternative. If you have fair skin or a family history of skin cancer, consulting your GP about sun protection and vitamin D supplementation is particularly worthwhile.