Deodorants, antiperspirants alter our skin bacteria

Wearing antiperspirant or deodorant could help manage your body odour but may also harm certain skin microbes that protect you against pathogens, a new study that suggests.

The researchers recruited 17 study participants - three men and four women who used antiperspirant products, which reduce the amount we sweat; three men and two women who used deodorant, which includes ethanol or other antimicrobials to kill off odour-causing microbes; and three men and two women who used neither product.

In an eight-day experiment all of the participants had swabs taken of their armpits between 11 am and 1 pm.

On day one, participants followed their normal hygiene routine in regard to deodorant or antiperspirant use. On days two through six, participants did not use any deodorant or antiperspirant. On days seven and eight, all participants used antiperspirant.

The researchers then cultured all the samples to determine the abundance of microbial organisms growing on each participant and how that differed day to day.

"We found that, on the first day, people using antiperspirant had fewer microbes in their samples than people who didn't use product at all," said Julie Horvath, of North Carolina Museum of Natural Sciences.

"In addition, people who used deodorant actually often had more microbes - on average - than those who didn't use product," Horvath said, who is also the an associate research professor at the North Carolina Central University.

By the third day, participants who had used antiperspirant were beginning to see more microbial growth. By day six, the amount of bacteria for all participants was fairly comparable.

"However, once all participants began using antiperspirant on days seven and eight, we found very few microbes on any of the participants, verifying that these products dramatically reduce microbial growth," Horvath said.

The researchers also did genetic sequencing on the samples. They found that, among study participants who had not worn deodorant or antiperspirant, 62 per cent of the microbes they found were Corynebacteria, followed by 21 per cent of various Staphylococcaceae bacteria, with a random assortment of other bacteria accounting for less than 10 per cent.

Corynebacteria are partially responsible for producing the bad smells we associate with body odour, but they are also thought to help us defend against pathogens.

Staphylococcaceae are among the most common microbes found on human skin and, while some can pose a risk to human health, most are considered beneficial.

The participants who had been regular antiperspirant users coming into the study had wildly different results.

Sixty per cent of their microbes were Staphylococcaceae, only 14 per cent were Corynebacteria, and more than 20 per cent were filed under "other" - meaning they were a grab-bag of opportunistic bacteria.

The study was published in the journal PeerJ.