According to the FDA, approximately one in a hundred persons may undergo an allergic reaction to the chemicals in cosmetics, so Rinzler's guide to ingredients, which translates all those polysyllables into comprehensible terms, may be much appreciated by the blotchy-skin set. Neither chemist nor cosmetician, she has read through the literature, consulted professionals, and badgered the companies for information--some of which will appear shortly on all labels. Part One characterizes kinds of products (the contents of and differences between lip gloss and lipstick) and suggests what ""natural"" substances can substitute for irritating ones--mineral oil can act as an emollient. Part Two lists the ingredients alphabetically and indicates common uses, possible side effects, and toxic dosage (if any): wheat starch, the thickener in Ultralash, ""can irritate eyes and produce symptoms similar to hay fever."" Rinzler also includes positive and negative research results (dehydroacetic acid, a preservative, is ""a carcinogen when injected under the skin of laboratory rats"") and takes a cautious--hut not preachy--view overall. For the allergy-prone, one of those instant necessities, but expect the powder-mongers to spot blemishes.