Based on what we know today, using a sunscreen with a sun protection factor (SPF) of 15 or higher is safer than doing without one when you're in the sun. Some of the chemicals used, specifically PABA (para-aminobenzoic acid) and oxybenzone, can be irritating. However PABA is no longer used as widely as it once was. Newer products containing Parsol 1789 are highly effective and appear less irritating. I have always recommended choosing sunblocks containing zinc oxide or titanium dioxide, both inert, opaque compounds that block almost the entire spectrum of the sun's damaging rays without causing irritation. (You can also use zinc oxide alone. Once available only in chalky white, it now comes in colorless form - as well as in various electric colors. Zinc oxide acts as a mechanical, rather than chemical, sun barrier.)
I'm aware of alarming reports on the Internet claiming that chemicals in sunscreen may have harmful estrogenic activity. These stem from a study of rats in Switzerland published in the March 2001 issue of Environmental Health Perspectives, but even the author of the study has said that no conclusions about the risk of cancer can be drawn from her findings to date.
In fact, the greatest danger of sunscreen appears to be the false confidence many people have in its protective powers. People often burn because they don't reapply as recommended after swimming or because they don't use enough sunscreen to begin with - you need at least one ounce (enough to fill a shot glass) to completely cover exposed areas of the body.
If you're concerned about the chemicals in sunscreen, be sure to take other precautions to protect yourself from the sun. Your best bet is to stay out of the sun, particularly between 10 a.m. to 2 p.m. standard time from April through September in the Northern Hemisphere. Specially manufactured sun protective clothing offers outstanding chemical-free protection and is a wise investment for your skin. A wide-brim hat and sunglasses are also effective measures. (Make sure your sunglasses block at least 99 percent of UVA and UVB radiation).
I see the threat of skin cancer as far higher than any theoretical risk posed by the chemicals sunscreen contains. Skin cancer is increasing at an alarming rate due to the cumulative effects of sunburns and sun tanning, which is also a sign of skin damage. Choose whatever form of sun protection you prefer, but definitely keep something between your skin and the sun.
Andrew Weil, M.D.