1. Choose mineral sunscreens listing zinc oxide or titanium dioxide as the active ingredients. Alternatively, if you cannot stand mineral based sunscreens, choose Mexoryl SX (ecamsule) or avobenzone, which have safer profiles than other “chemical” sunscreen ingredients. All of these ingredients offer some protection against both UVA and UVB rays.
2. Avoid Retinyl Palmitate (or retinol), a form of vitamin A which may actually accelerate the growth of cancerous cells in the presence of sunlight.
3. Avoid oxybenzone or 4-MBC, known hormone disruptors.
4. Avoid spray formulations, which are easily inhaled (and likely to be absorbed), with unknown consequences (these sunscreens are approved by the FDA for topical application only, and are not tested when absorbed through lungs).
An excellent resource is the Environmental Working Group website, which has a more thorough discussion of nanoparticles in sunscreens, ingredient toxicities, and ratings for many sunscreens currently available in US: http://breakingnews.ewg.org/2011sunscreen/
BOTTOM LINE: We use only mineral based sunscreens and find that All Terrain Aqua Sport SPF 30 (active ingredient=zinc oxide 16%) goes on easily, has no scent and offers excellent sun protection. We buy ours online, but this brand is available at most Whole Foods or other specialty health food stores.