Final answer:
A cosmetic is applied to beautify or alter appearance without affecting the body's functions, while a drug is used to treat, prevent, or diagnose diseases or affect body functions.
Step-by-step explanation:
The primary difference between a cosmetic and a drug, according to the U.S. Food and Drug Administration (FDA), lies in the products' intended uses and effects on the body. A cosmetic is defined as a product applied to the human body for cleansing, beautifying, promoting attractiveness, or altering the appearance without affecting the body's structure or functions. In contrast, drugs are products meant to diagnose, cure, mitigate, treat, or prevent disease, or to affect the structure or any function of the body.
While cosmetics, such as most deodorants, are generally not subject to FDA premarket approval, drugs must undergo a rigorous approval process, including testing for safety and effectiveness. Antiperspirants, for example, are considered over-the-counter drugs because they affect the body's function by reducing sweat production. The FDA also plays a role in regulating cosmetics to ensure labeling accuracy and implement safety measures, but its powers are more limited compared to those wielded in drug regulation.