Deodorants are substances applied to the body, particularly the armpits, mainly to reduce body odor caused by the bacterial breakdown of perspiration. A subgroup of deodorants are "antiperspirants", which prevent odor and reduce sweat produced by parts of the body. Antiperspirants are typically applied to the underarms, while deodorants can also be used on feet and other areas in the form of body sprays.
Human sweat itself is largely odorless until it is fermented by bacteria. Bacteria thrive in hot, humid, acidic environments. The human underarm is among the consistently warmest areas on the surface of the human body, and sweat glands provide moisture, which when excreted, has a vitally cooling effect. When adult armpits are washed with pH basic soaps, the skin loses its acid mantel (pH 4.5 - 6), raising the pH to become basic. Bacteria thrive in high pH or base environments. Creating such an environment in the armpit makes it more susceptible to bacterial colonization. The bacteria feed on the sweat from the apocrine glands and on dead skin and hair cells, releasing 3-methyl-2-hexenoic acid in their waste, which is the primary cause of body odor. It is healthy and necessary to sweat. Underarm hair is designed to wick the moisture away from the skin and aids in keeping the skin dry enough to prevent or diminish bacterial colonization. The hair is less susceptible to bacterial growth and therefore is ideal for preventing the bacterial odor
Deodorants — classified and regulated as over-the-counter (OTC) cosmetics by the U.S. Food and Drug Administration (FDA) — are designed to eliminate odor. The first commercial deodorant, Mum, was introduced in the late nineteenth century. Deodorants are usually alcohol-based. Alcohol initially stimulates sweating, but may also temporarily kill bacteria. Deodorants can be formulated with other, more persistent antimicrobials such as triclosan, or with metal chelant compounds that slow bacterial growth. The skin of the armpit is highly thin and absorbant. Antibacterial toxins in deodorants may pose a danger to health when absorbed into the body. Deodorants may contain perfume fragrances intended to mask the odor of perspiration.
Deodorants may be combined with antiperspirants — classified as drugs by the FDA — which attempt to stop or significantly reduce perspiration and thus reduce the moist climate in which bacteria thrive. Aluminium chloride, aluminium chlorohydrate, and aluminium-zirconium compounds, most notably Aluminium zirconium tetrachlorohydrex gly and Aluminium zirconium trichlorohydrex gly, are the most widely used antiperspirants. Aluminium-based complexes react with the electrolytes in the sweat to form a gel plug in the duct of the sweat gland. The plugs prevent the gland from excreting liquid and are removed over time by the natural sloughing of the skin. The blockage of a large number of sweat glands reduces the amount of sweat produced in the underarms, though this may vary from person to person.
The modern formulation of the antiperspirant was patented by Jules Montenier on January 28, 1941. This patent solved the problem of the excessive acidity of aluminium chloride and its excessive irritation of the skin, by combining it with a soluble nitrile or a similar compound. This formulation was first found in "Stopette" deodorant spray, which Time Magazine called "the best-selling deodorant of the early 1950s". . "Stopette" gained its prominence as the first and long-time sponsor of the game show What's My Line?, and was later eclipsed by many other brands as the 1941 patent expired.
A popular alternative to modern commercial deodorants is ammonium alum, which is a common type of alum sold in crystal form. It has been used as a deodorant throughout history in Thailand, the Far East, Mexico and other countries. 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.
An experiment with mice found that applying an aqueous solution of aluminum chloride to the skin resulted in "a significant increase in urine, serum, and whole brain aluminum." Other experiments on pregnant mice showed transplacental passage of aluminum chloride.
NCI discusses two studies that address the breast cancer claims: A 2002 study of over 800 patients at Fred Hutchinson Cancer Research Institute that found no link between breast cancer and the use of antiperspirant/deodorant; and a study of 437 cancer patients, published in 2003 by the European Journal of Cancer Prevention, which found a correlation between earlier diagnosis of breast cancer and antiperspirant/deodorant use. The NCI's analysis of the second study said that it "does not demonstrate a conclusive link between these underarm hygiene habits and breast cancer. Additional research is needed to investigate this relationship and other factors that may be involved.
One school of thought, advanced by the studies of researcher Dr. Phillipa Darbre, hypothesizes that particular substances in deodorants, such as preservatives called parabens, or salts such as aluminum chloride used in antiperspirants, get into the bloodstream or accumulate in breast tissue, where they enhance or emulate the effects of estrogen, which stimulates the growth of cancerous breast cells. The ACS and other scientists consider these studies to be early and inconclusive, but merit further research; Darbre also stated that her findings did not show causality. The main reservations have to do with the source and significance of the parabens or other toxic substances. Michael Thun, MD, of the ACS argued that even if some of the substances in antiperspirants do promote tumor growth, the risk from cosmetic use appears minuscule compared with other known tumor promoters — from 500 to 10,000 times less potent than taking oral estrogen or being obese. Kris G. McGrath, MD, continues to point out the relationship between antiperspirants / deodorants and breast cancer. One of his studies published in 2003 revealed a significant earlier age of diagnoses in those women who more frequently used antiperspirants and shaved their underarms, than those women who less frequently did these habits and especially than those who did not use these products or shave.
Cultures and individuals differ in their beliefs about the need for deodorant, and on whether bodily odors are offensive. Various foods such as garlic may also affect body odor.
Commercially-manufactured deodorants may also target areas of the body other than the armpits, such as the genitals, and particularly the female genitals. Such products are sometimes the target of sexually graphic humor.