Dark Side Of Deodorants

A rather shocking discovery has recently come to light: antiperspirant and deodorants can significantly alter the type and number of beneficial microbes that inhabit our underarms. Such findings strictly contradict the common belief that our microbes have naturally co-evolved with us; apparently, our evolving habits have resulted in the alterations.

Researchers at North Carolina State University, the North Carolina Museum of Natural Sciences, North Carolina Central University, Rutgers University and Duke University have found that antiperspirants and deodorants can potentially influence the quantity and type of bacterial populations found in the human armpit ‘microbiome’.

Corresponding author Julie Horvath, Head of the Genomics and Microbiology Research Laboratory at the NC Museum of Natural Sciences and an Associate Research Professor at NC Central stated that the purpose of the study was to understand the various effects of these products on the microbial ecosystem that resides on humans. “Ultimately, we aim to decipher whether these changes are good or bad, but first, we have to understand what the landscape is and how our daily habits influence it”. The work is published in the journal PeerJ.

The Human Microbiome: Dark Side Of  Deodorants

Co-author Rob Dunn, a Professor of Applied Ecology at NC State explained that thousands of bacterial species have the potential to inhabit human skin, particularly the armpits. Understanding exactly which species reside in a particular armpit has been difficult to predict. However, the current findings have revealed the use of deodorant and/or antiperspirant to be one of the major determinants in this aspect.

“During the last century, the use of underarm products has fairly escalated for the majority of Americans”, stated co-author Julie Urban, Assistant Head of the Genomics and Microbiology Laboratory at the NC Museum of Natural Sciences, and Adjunct Professor of Entomology at NC State. Whether the use of these products is beneficial or harmful for human microbiome has not been considered, and still remains an intriguing area for research.

Unraveling The Mystery: Study Design

Researchers recruited 17 participants in a study that investigated the microbial impact of deodorants and antiperspirants. They were divided as follows: four women and three men who used antiperspirants; two women and three men who used deodorants including ethanol or other antimicrobials to eliminate odor-causing microbes; two women and three men who used neither product. An eight-day experiment was conducted during which swabs were taken daily from the armpits of all participants between 11 am and 1 pm.

On day one, the participants were instructed to follow their usual hygiene routine with respect to the use of deodorants and antiperspirants. For the next five days, they were asked not to use any product. On the last two days, all of them used antiperspirants. All swabs were then cultured to determine how the amount of microbial organisms growing on each participant differed during the course of the experiment.

Correlating The Use Of Underarm Products With Bacterial Populations

“We saw that on the first day, the samples from participants using antiperspirant had fewer microbes as compared to those who did not use any product. However, there was a marked variability which made it hard to draw solid conclusions”, explained Horvath. “Moreover, people who used deodorants often had more microbes on average as compared to those who did not use both products”.

By the third day, those using antiperspirants showed more microbial growth. By the sixth day, the number of bacteria form all participants was fairly comparable. However, once all participants started to use antiperspirants on the last two days, the samples showed significantly reduced microbial growth, hence demonstrating that these products potentially alter and inhibit growth of underarm microbiome.

Dark Side Of Deodorants: Involving Genetics

Going a step further for determining the effect of these products on microbial biodiversity (composition and variety of bacteria with time), the researchers genetically sequenced all the samples taken on day three and day six.

It was seen that the participants who didn’t use either product had a 62 percent population of ‘Corynebacteria’, a 21 percent population of ‘Staphylococcaceae’ bacteria, and a remaining less than 10 percent of random mixture of bacterial populations. Even though ‘Corynebacteria’ are generally responsible for causing body odor, they are also beneficial in defending against pathogens. ‘Staphylococcaceae’ are the most common form of bacteria residing on human skin, and most populations are considered beneficial.

On the contrary, the participants dedicated to using antiperspirants had extremely different results – 60 percent populations were those of ‘Staphylococcaceae’, 14 percent were ‘Corynebacteria’ and 20 percent were characterized as ‘others’, possibly opportunistic bacteria.

The Conclusion

Based on their findings, researches state that using antiperspirants and deodorants significantly rearranges the microbial ecosystem of human skin. What’s dangerous is that the repercussion of this effect on our health remains unknown. This is a question that requires further investigation to be answered.

Also, these results highlight how evolving human behavior, such as bathing etc, can have a profound, even unintentional, impact on microbial organism inhabiting human skin

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