Melanomas were virtually unheard of before the introduction of tanning agents in the 1940s. Since then, the rate of melanoma has risen faster than any other cancer type. Meanwhile, parents slather sunscreen over their children's bodies and send them out into the sun, believing that they are safe." Similarly, adults seek a tan, believing it's "healthy" as long as they are "protected" with sunscreens. To the contrary, there is evidence that sunscreen use may actually cause melanomas. Researchers counted the nevi (pigmented skin moles) in 631 kids, then interviewed their parents about their sunscreen use. After adjusting for latitude and skin type, those who used the most sunscreen had the most moles, while those who used the least sunscreen and instead wore protective clothing had the fewest.*
Ozone depletion may play some role in the higher melanoma rate, but the rate began to go up long before ozone depletion became an issue. Recently manufacturers have touted "broad-spectrum" sunblocks, which reflect more of the rays that penetrate more deeply into the skin, but no claims or studies have been made that suggest that melanomas can be prevented in this way. Meanwhile, most dermatologists, epidemiologists, and sunscreen makers continue to remain mute about the connection between sunscreens and melanoma. With a multimillion-dollar market at stake, the sunscreen industry in particular has an interest in keeping these facts out of the public eye, and little research is being funded.
The only true protection is found in avoiding the sun, especially during the middle of the day (10 AM to 4 PM during daylight savings time). If you must venture out, stay in the shade or wear a hat and other protective clothing.
* Autier, P., et al., "Sunscreen Use, Wearing Clothes, and Number of Nevi in 6- to 7-Year-Old European Children," J. Nat. Cancer Inst.