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

UV radiation from both the sun and tanning beds is a well-established, causal risk factor for skin cancer. Between 60 and 70 percent of all melanomas are attributed to UV radiation. Skin cancer is the most common cancer in the world, and its incidence is still rising. This is not a statistical suspicion but a causal relationship that is broadly supported by the research.

Tanning beds are not a safe alternative to the sun in this regard. Using a tanning bed causes the same damage as excessive sun exposure: UV light damages the DNA of skin cells, suppresses the skin's local immune system, and causes inflammation. These three mechanisms -- DNA mutations, immune suppression, and inflammatory responses -- are precisely the steps that lead to melanoma formation. The more frequently and the longer someone uses a tanning bed, the greater the cumulative damage.

At the same time, some sun exposure is biologically necessary. The skin produces vitamin D under the influence of UVB radiation, and more than half of the world's population is at risk of vitamin D deficiency, partly because people spend too little time outdoors. A deficiency of vitamin D is associated with bone disorders (rickets in children, osteoporosis and fractures in adults) and possibly also with an increased risk of certain cancers, autoimmune diseases, infectious diseases, and cardiovascular disease, although the evidence for the latter is not equally well established for all conditions.

The question 'how much sun is safe?' therefore has no simple universal answer. How much vitamin D a person produces depends on skin pigmentation, age, time of day, season, latitude, and whether sunscreen is used. People with lighter skin produce vitamin D more quickly but also burn more quickly; people with more skin pigmentation need more exposure to achieve the same level of production. A rough rule of thumb used in the research is: short, regular exposure of the face, arms, and hands outside peak hours, without burning. Sunburn is the clearest sign that the damage threshold has been exceeded.

Prevention works. Public campaigns that inform people about sensible sun exposure have led to a noticeable decline in melanoma mortality, even though the total number of new cases is still rising. Most skin cancers are preventable, according to the researchers. In practical terms this means: avoid sunburn, steer clear of tanning beds, and use protective clothing and sunscreen in bright midday sun, without completely avoiding the moderate daily exposure needed for vitamin D production.