Few people would whip out a chemistry set, uncork the vials, and slap the compounds on their face. Yet, millions of women and girls essentially do that every day when they unzip their makeup bags and apply lipstick, mascara, and other makeup. Like the compounds in a chemistry set, makeup consists of chemicals. Although the chemicals in cosmetic products are intended to improve the appearance of skin, lips, and lashes, some can cause adverse effects.

Brushing up on makeup chemistry isn't hard: If you can read a label, you are halfway there. The U.S. Food and Drug Administration (FDA) requires cosmetics manufacturers to put labels on makeup listing ingredients in descending order of weight. Ingredients that make up less than 1 percent of the makeup item, such as fragrance or colorants, are listed after other ingredients, not in descending order of weight.

The payoff from even a little bit of learning can be big. A savvy makeup user reduces her chances of developing rashes, eye infections, acne, and other health problems linked to cosmetics. She also is less likely to waste money on expensive cosmetics with formulas similar to those of less costly brands.

The first lesson in cosmetic chemistry is that most makeup ingredients are intended to give the product its color and consistency. A few basic classes of ingredients—coloring agents, bases, bulking agents, sunscreens, and additives—are common to many kinds of makeup.