Human perspiration is largely odorless until it is fermented by bacteria that thrive in hot, humid environments. The human underarm is among the most consistently warm areas on the surface of the human body, and sweat glands provide moisture, which when excreted, has a vital cooling effect. When adult armpits are washed with alkaline pH soap, the skin loses its acid mantle (pH 4.5 – 6), raising the skin pH and disrupting the skin barrier. As many bacteria thrive in this elevated pH environment, this makes the skin susceptible to bacterial colonization. The bacteria feed on the sweat from the apocrine glands and on dead skin and hair cells, releasing trans-3-Methyl-2-hexenoic acid in their waste, which is the primary cause of body odor. Underarm hair wicks 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.
After using a deodorant containing zirconium, the skin may develop an allergic, axillary granuloma response. Antiperspirants with propylene glycol, when applied to the axillae, can cause irritation and may promote sensitization to other ingredients in the antiperspirant. Deodorant crystals containing synthetically made potassium alum were found to be a weak irritant to the skin. Alcohol-free deodorant is available for those with sensitive skin. Frequent use of deodorants was associated with blood concentrations of the synthetic musk galaxolide.
Aluminum is present most often in antiperspirants in the form of aluminum chlorohydrate. Aluminum chlorohydrate is not the same as the compound aluminum chloride, which has been established as a neurotoxin. At high doses, aluminum itself adversely affects the blood–brain barrier, is capable of causing DNA damage, and has adverse epigenetic effects.
The Food and Drug Administration, in a monograph dedicated to analysing the safety of deodorants, concluded that “despite many investigators looking at this issue, the agency does not find data from topical and inhalation chronic exposure animal and human studies submitted to date sufficient to change the monograph status of aluminum containing antiperspirants”, therefore allowing their use and vowing to keep monitoring the scientific literature. Members of the Scientific Committee on Consumer Safety (Europe) concluded that “due to the lack of adequate data on dermal penetration to estimate the internal dose of aluminium following cosmetic uses, risk assessment cannot be performed.”
The myth that breast cancer is linked with deodorant use has been widely circulated, and appears to originate from a spam email sent in 1999; however, there is no evidence to support the existence of such a link. One constituent of deodorant products which has given cause for concern are parabens, a chemical additive. According to the American Cancer Society “studies have not shown any direct link between parabens and many health problems, including breast cancer”.
The FDA has “acknowledged that small amounts of aluminium can be absorbed from the gastrointestinal tract and through the skin.”, leading to a warning “that people with renal dysfunction may not be aware that the daily use of antiperspirant drug products containing aluminium may put them at a higher risk because of exposure to aluminium in the product.” The agency warns people with renal dysfunction to consult a doctor before using antiperspirants containing aluminum.