Deodorants, however, don't stop you from sweating. Instead, deodorants use antimicrobials to kill bacteria and slow their growth. Bacteria crowd under your arms, with 1 million of the tiny creatures living on every square centimeter or so of skin. Although a deodorant can never be an antiperspirant, an antiperspirant can be a deodorant. That's because some antiperspirants have antimicrobial ingredients [sources: Poucher, Antiperspirants Info].
One of the main ingredients is triclosan, a common biocide that is also found in plastics, textiles, toothpaste, antibacterial soaps, cosmetics and body washes. Triclosan takes aim at the cell wall of the bacteria, killing the smelly beasts [source: U.S. FDA, Antiperspirants Info].
Although the U.S. Food and Drug Administration says triclosan is not harmful to humans, some studies indicate that the chemical alters the regulation of hormones in animals. Other studies suggest the chemical helps make bacteria resistant to antibiotics [source: U.S. FDA, Yazdankha et al.].
Polyhexamethylene biguanide is another active ingredient in deodorants. PHMB, as it is called, is an effective bacteria killer and is often used as a disinfectant in swimming pools and hot tubs. It does a good job of wiping out bacteria that cause adenovirus ocular infections. Moreover, alcohol, another ingredient, is also effective at killing bacteria [source: Antiperspirants Info, Romanowski et al.].
Still, do we really need deodorants and antiperspirants? Some people apparently don't. Researchers at the University of Bristol in Great Britain found that 75 percent of people they studied had a particular version of a gene that doesn't produce underarm odor. Nevertheless, these people used deodorants and antiperspirants. Moreover, those with the gene variation didn't have sticky ear wax, which apparently is a good indication of whether someone's armpits smell [source: Science Daily].
Keep reading for a plethora of information on your underarms.