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Tag: armpit bacteria

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Another interesting study that makes you think about our microbiome. From NPR:

Stinky T-Shirt? Bacteria Love Polyester In A Special Way

Anyone with a drawerful of T-shirts knows that the synthetic ones can get sour after just a brief jog, while old-school cotton T-shirts remain relatively stink-free all day. And now science explains why. The bacteria that flourish on a sweaty polyester T-shirt are different from those that grow on cotton, researchers at the University of Ghent in Belgium found. Polyester makes a happy home for Micrococcus bacteria, while Staphylococcus, a common armpit denizen, was found on both poly and cotton.

Microbes love the cozy warmth of the human armpit; it's like a trip to the tropics without ever having to leave home. And it's crowded in there. Those microbes eat compounds in sweat and generate odors, which support a flourishing deodorant industry. 

The scientists asked 26 volunteers to take a spinning class while wearing shirts made of cotton, poly or blends. The shirts were then incubated for a day, and the microbes extracted and DNA fingerprinted. Volunteers also had their armpits swabbed. 

It turns out the bugs on the shirts are different from the bugs in the pits. While Corynebacterium is thought to be the main cause of armpit body odor, there was no Corynebacterium on the clothes. Instead, Staphylococcus flourished on cotton and poly, and Micrococcus, bacteria also known for making malodor, loved polyester.

He's also trying to help people with excessive body odor by giving them armpit bacteria transplants. "We have done transplants with about 15 people, and most of them have been successful," Callewaert, a Ph.D. student in applied biological sciences at the University of Ghent, tells Shots. "All have had an effect short term, but the bad odor comes back after a few months for some people."

Manufacturers have tried to make polyester fabric less hospitable to bacteria by impregnating it with antimicrobials like silver nanoparticles or triclosan. Both products have been criticized as having potentially negative impacts on the environment, and there are few data on how they might affect the wearer. Callewaert thinks the ultimate solution will be something more organic — supplant bad bugs with good ones. 

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An interesting small study of the human armpit bacterial community. From Real Clear Science:

Antiperspirants Alter Your Armpit Bacteria and Could Actually Make You Smell Worse

In modern society, antiperspirants are widely hailed as a godsend, dispelling the inconvenient odors wafting from armpits everywhere. But a new study casts doubts on their vaunted position. As it turns out, antiperspirants may actually make you smell worse in the long run.

For 90% of all Americans, slathering on deodorants and antiperspirants is a daily occurrence, a precautionary measure against foul odors and unsightly sweat stains. The odors arise when bacteria living in our armpits break down lipids and amino acids excreted in sweat into more smelly substances. Deodorants employ antimicrobial agents that kill off bacteria, as well as chemicals that replace noxious odors with pleasant aromas. Deodorants that double as antiperspirants, like Degree, Old Spice, and Dove, take the process one step further by physically plugging sweat glands with aluminum-based compounds.

While most of us might only concern ourselves with the dry, aromatic benefits of antiperspirants and deodorants, researchers at the Laboratory of Microbial Ecology and Technology at the University of Ghent in Belgium are more interested in the effects on bacteria. Billions of bacteria dwell in the "rain forests" under our arms, and the substances we don are mucking with their habitats!

To uncover how deodorants and antiperspirants affect armpit bacteria, Chris Callewaert, a Ph.D student specializing in microbial ecology, and a team of researchers recruited eight subjects for a task a great many people (and especially their friends) might deem unbearable: Six males and two females pledged not to use deodorant or antiperspirant for an entire month. Specifically, four subjects stopped using their deodorants and another four stopped using their antiperspirant deodorant. (Most antiperspirants are also deodorants. See image below for an example.) Another control subject who did not regularly use either was asked to use deodorant for a month. The duration was chosen because it takes approximately 28 days for a new layer of skin cells to form.

The researchers analyzed the diversity and abundance of subjects' armpit bacteria at various timepoints before they stopped using antiperspirant, during the period of abstaining from antiperspirant, and for a few weeks after resuming the use of antiperspirant. Switching hygiene habits plainly altered the armpit bacterial communities of every subject. Since no two armpits and their resident bacteria are identical, it was difficult to pinpoint precise changes brought about by deodorants or antiperspirants, but one clear trend did materialize: antiperspirants resulted in a clear increase of Actinobacteria.

You might not recognize the name of Actinobacteria, but chances are, you've smelled them. Dominated by Corynebacterium, they are the major instigators of noxious armpit odor. Other microbes that inhabit the armpit, like Firmicutes and Staphylococcus, don't produce odors as quickly, nor are those odors nearly as pungent.

Callewaert believes the aluminum compounds in antiperspirants may be to blame, killing off "good," less smelly bacteria and allowing "bad" bacteria to dominate. His study found that deodorants which lack these sweat-blocking antiperspirant compounds are actually linked to a slight decrease of stinky Actinobacteria.

Though antiperspirants and deodorants are widely used, they are only a temporary fix."The measures we utilize today do not take away the initial source: the odor causing bacteria," Callewaert told RealClearScience. "Deodorants only mask unpleasant odors. We can do better than that. The follow up of this research is finding better solutions."

And Callewaert is already working on one: "armpit bacterial transplantation"."We take away the bad bacteria from the armpit of somebody with a body odor, and replace it with the good bacteria of a relative who doesn't have a body odor," he explained."So far we have helped over 15 people. For most subjects it brings immediate improvements. Most of them on a permanent time scale, although there are also people who suffer again from a body odor after some months."