Cosmetics that treat or prevent diseases are also drugs. Products such as dandruff shampoo, fluoride toothpaste, and antiperspirant deodorant are both cosmetics and drugs. A good way to tell if you're buying a cosmetic that is also a drug is to see if the first ingredient listed is an "active ingredient." The active ingredient is the chemical that makes the product effective. The manufacturer must have proof that it's safe for its intended use.