The use of deodorants and antiperspirants to wipe out odour-causing bacteria may alter the skin microbiome, increasing its diversity, according to a new study.
People who use antiperspirants seem to have a more diverse group of bacteria on their underarms, compared with those who only use deodorant or nothing at all – even though antiperspirants reduce the total number of bacteria drastically, the researchers found.
Dr. Julie Horvath, head of the genomics and microbiology research lab at North Carolina’s Museum of Natural Sciences, part of NC State University, said that the aim of the new study is to find whether changes in people’s microbial ecosystem are bad or good.
A 2001 paper that was published in the journal Clinics Dermatology, found that about 90 percent of adults in the United States use deodorants or antiperspirants. Deodorants kill off bacteria directly using antimicrobial substances, while antiperspirants block sweat glands using aluminium salts – which reduce perspiration and also live odour-causing bacteria without the nutrients they need to survive.
For the new research – published Tuesday (Fec. 2) in the journal PeerJ – seventeen study participants – who used either antiperspirants, deodorants, or nothing at all – had to undergo armpit swabs for a total of eight days. On the first day, they all had to follow their usual underarm routine.
From day two until day six, they had to use nothing at all, and on days seven and eight, the participants were instructed to apply an antiperspirant – Old Spice Fiji for men, and Secret Powder Fresh for women, the researchers said.
Every day, the researchers took samples of bacteria found on each individual’s underarms. To find the types of bacteria species, they then sequenced the bacterial genomes. The results showed that on the last product-free day of the study, the participants had on average about 750 units of bacteria. On the first day of antiperspirant use (seventh day of the study), the colony-forming units of bacteria dropped to 73, and on the eighth day they decreased even further to only 25.
Two days after not using deodorants and antiperspirants, the participants had 22 species of bacteria on their underarms. However, on the fifth day, the bacteria species increased to 106, the researchers found.
People who did not use antiperspirants or deodorants even before the study started, had eight percent Anaerococcus, 21 percent Staphylococcaceae, 62 percent Corynebacterium, and nine percent of bacteria from other genuses.
Study participants who used antiperspirants before the study had four percent Anaerococcus, 14 percent stinky Corynebacterium, 60 percent Staphylococcaceae, and 22 percent other genuses. Deodorant users had five percent Anaerococcus, 29 percent Corynebacterium, 61 percent Staphylococcaceae, and five percent other, according to the researchers.
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