armpit bacteria

Recent years have seen an increasing interest in understanding how the use of commercial products for hygiene and other purposes affects the human body.

 

Some research in this area has examined variations in bacterial communities (microbiome) present in various body structures, such as the saliva, the skin, and the digestive tract. While variations in bacteria exist naturally from one individual to another, scientists are interested in understanding how those variations may be increased, decreased, or otherwise influenced by the presence of products we use every day.

In one recent study, researchers looked at how armpit bacteria are affected by the use of antiperspirant and deodorant. The study compared armpit bacteria among three groups of individuals: those who typically use only antiperspirant, those who use only deodorant, and those who normally use no products at all. Samples of armpit bacteria were taken from all three groups. Participants who normally used antiperspirant and deodorant were then asked to stop using any products for a period of eight days, during which time samples were again taken. Sample collection was also done for a short period after participants resumed use of their chosen products.

Researchers examined the samples to identify changes not only to the overall quantity of bacteria, but also to the types of bacteria, and the number of different bacterial varieties present in the sample.. Several results were observed:

    • Samples taken before ceasing product use showed that antiperspirants reduced the quantity of bacteria, while deodorants did not appear to affect quantity significantly;
    • The quantity of bacteria increased about two days after ceasing antiperspirant use and eventually reached levels similar to individuals who regularly do not use any product;
    • Antiperspirant users also showed a greater variety of bacteria upon ceasing product use than either deodorant users or individuals using no product
    • Individuals who used antiperspirants or deodorants long-term, but who stopped using products for two or more days, had armpit communities dominated by Staphylococcaceae, whereas individuals who habitually used no products were dominated by Corynebacterium;
    • Upon resuming product use, bacterial quantities for antiperspirant users again declined dramatically.

 

Researchers believe that the different effects of antiperspirant versus deodorant on quantity of bacteria are explained by two key differences between the products: (1) many deodorants are ethanol-based and likely more water soluble, thus easier to wash away than antiperspirants; and (2) antiperspirants contain aluminum-based salts that physically block sweat glands, thus reducing resources necessary for the growth of bacterial communities.

The wider variety of bacteria present in antiperspirant users after ceasing use is suspected to result because antiperspirant dramatically reduces quantities of the dominant bacterial species, thereby creating more opportunities for rare species to become established. Researchers had expected to observe this effect with deodorant users as well, but in fact found that deodorant users actually had fewer species of bacteria in their armpits compared to participants who used no product.

 

 

Urban J, Fergus DJ, Savage AM, Ehlers M, Menninger HL, Dunn RR, Horvath JE. (2016) The effect of habitual and experimental antiperspirant and deodorant product use on the armpit microbiome. PeerJ 4:e1605

 

 

 

 

 

 

Written by Linda Jensen

 

 

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