From what I've seen and read, the new mineral-based makeup powders look good. The products seem to impart a natural look to the skin that doesn't seem "made up" and, from what I've been able to determine, are safe to use and may be less irritating than more conventional foundations and other cosmetics used on the skin.
Mineral makeup powders contain zinc oxide, titanium dioxide, mica and iron oxides. The only one of these I'm concerned about is titanium dioxide that has been "micronized" or reduced to "nanoparticles" one millionth of a millimeter in size. Some studies have indicated that when exposed to light, titanium dioxide nanoparticles may prompt formation of free radicals that could damage cells, and others have suggested that the tiny particles of this mineral can enter the brain and cause oxidative stress (most particles are too big to penetrate the blood-brain barrier). While evidence is far from certain that titanium dioxide nanoparticles present any danger, to be safe, I would steer clear of cosmetics with "micronized titanium dioxide" listed on the labels. I also suggest checking labels to be sure that no undesirable chemicals have been added in to a mineral-based cosmetic you're considering. You might log on to the Web site of The Green Guide Institute at www.thegreenguide.com for a list of cosmetic products that contain larger, safer mineral particles. The nonprofit Environmental Working Group, www.ewg.org, lists on its Web site 250 personal care products that contain one or more of 57 types of nanoparticles that the organization deems "poorly studied" and potentially hazardous.
Some manufacturers add synthetic materials to mineral powders to help them spread more evenly, but I haven't seen any evidence suggesting that these are harmful.
Andrew Weil, M.D.