Many skin cancers are a direct result of overexposure to the UV rays in sunlight. Both basal cell and squamous cell cancers (the most common types of skin cancer) tend to be found on sun-exposed parts of the body, and their occurrence is typically correlated to lifetime sun exposure. The risk of melanoma, a more serious but less common type of skin cancer, is also related, albeit more weakly, to sun exposure. Skin cancer has also been linked to exposure to some artificial sources of UV rays, such as the exposure one receives in a tanning bed. Therefore, care should be taken to not overexpose our bodies to UV, and when we plan to be in the sun for extended time, use of a sunscreen is imperative.
However, be careful of which sunscreens you use. Studies of six common sunscreen chemicals, five of them exerted significant estrogenic activity, as measured by the increase in proliferation rates of human breast cancer cells (MCF-7 cells) grown in vitro. These chemicals were 3-(4-methylbenzylidene)-camphor (4-MBC), octyl-methoxycinnamate (OMC), octyl-dimethyl-PABA (OD-PABA), bexophenome-3 (Bp-3) and homosalate (HMS). The results for 4-MBC have been replicated in other laboratories.
The current body of evidence suggests that zinc oxide macroparticles are safest and most efficacious for blocking the harmful rays of the sun.