Ask Pablo: Does Sunscreen Cause More Skin Cancer Than It Prevents? at TreeHugger:

Dear Pablo: I have heard that sunscreen actually causes more skin cancer than it prevents. Is there any truth to this?

It sounds unbelievable but there is actually some truth here. The Environmental Working Group is releasing their 2010 Sunscreen Guide, in which they independently tested 1400 SPF-rated products, including beach and sports lotions, sprays and creams, moisturizers, make-up and lip balms. Only 8% of the beach and sport sunscreens (39 out of 500) offer sufficient protection and healthier ingredients to earn the EWG's "green" rating. There are two main concerns about sunscreen; the false sense of protection that they offer, and the chemicals that they contain.

Some good science and good advice here, such as,

# Look for sunscreens with avobenzone, Mexoryl, titanium dioxide, and zinc for UVA coverage.
# Avoidance is best. If you don't have to be out in the sun between 10am and 4pm, stay in the shade.
# The best sunscreen is the kind you wear. Outdoor clothing manufacturers are producing SPF-rated clothing to keep you comfortable and sunburn free.

The Sunscreen Guide leads with,

EWG's fourth annual Sunscreen Guide gives low marks to the current crop of sunscreen products, with a few notable exceptions. EWG researchers recommend only 39 - 8 percent - of 500 beach and sport sunscreens for this season.

The reason? A surge in exaggerated SPF claims above 50 and new disclosures about potentially hazardous ingredients, in particular recently developed government data linking vitamin A to accelerated growth of skin tumors and lesions.