A deodorant is a substance applied to the body to prevent body odor caused by the bacterial breakdown of perspiration in armpits, feet, and other areas of the body. A subgroup of deodorants, antiperspirants, affect odor as well as prevent sweating by affecting sweat glands.

Antiperspirants are typically applied to the underarms, while deodorants may also be used on feet and other areas in the form of body sprays. In the United States, the Food and Drug Administration classifies and regulates most deodorants as cosmetics, but classifies antiperspirants as over-the-counter drugs.

Deodorants are classified and regulated as cosmetics by the U.S. Food and Drug Administration (FDA) and are designed to eliminate odor. Deodorants are often alcohol-based. Alcohol initially stimulates sweating, but may also temporarily kill bacteria.

Deodorants combined with antiperspirant agents are classified as drugs by the FDA. Antiperspirants attempt to stop or significantly reduce perspiration and thus reduce the moist climate in which bacteria thrive.Deodorants and antiperspirants come in many forms. What is commonly used varies in different countries. In Europe, aerosol sprays are popular, as are cream and roll-on forms. In the United States, solid or gel forms are dominant.

A popular alternative to modern commercial deodorants is ammonium alum, which is a common type of alum, also containing aluminum, sold in crystal form and often referred to as a deodorant crystal. It has been used as a deodorant throughout history in Thailand, the Far East, Mexico and other countries.