Armpit Ecology!

Why do we smell, and how does natural deodorant work?

As we all know, deodorants are big business! I’ve spent my fair share on commercial products over the years in trying to shut down the stink! But I have not used commercial deodorant now for many months, since I began making my own natural product.

Developing natural products requires knowledge of the processes behind the goal. With the goal of preventing BO naturally, I started mining the internet and experimenting. Our community of natural product users found that natural oils and butters combined with essential oils, cornstarch and baking soda can effectively combat stink. But how? And what happens in our armpits anyway to make us smell?

The armpit (“axillary” in medical speak) environment is moist, warm, dark, and loaded with organic matter,

(skin and sweat), which makes it a great home for microorganisms. Sweat glands in the armpits include apocrine, eccrine and possibly apoeccrine glands. Cartoon of eccrine and apocrine sweat glandsEccrine glands play an important role in regulating body temperature. They secrete water that contains salt ions (sodium, chloride, potassium, calcium & magnesium), amino acids, urea and other compounds[1]. Apocrine glands are stimulated by emotion and regulated by hormones. They open into the hair canal and secrete an oily mixture of proteins, lipids and steroids, the compounds most associated with body odor. Apoeccrine glands are proposed to develop from eccrine glands and to have similar watery secretions1.

Microorganisms living in the armpits use the organic sweat gland secretions as food,

and as they break down these molecules, volatile odor compounds are released[2]. Funny bacteria cartoonAntiperspirants contain aluminum compounds that interact with proteins in eccrine glands to create a gel-like substance that plugs the gland and prevents the sweat from escaping. To be classified as an antiperspirant, a product must reduce the amount of sweat produced by at least 20% in at least 50% of people tested under controlled conditions[3]. That seems like a pretty low reduction in sweat, and do we really want to block our bodies from this natural process anyway? Sweat still escapes, and with it the food for our underarm microbes, so it’s likely that the masking effect of perfumes in antiperspirants plays a larger role in how these products improve odor. Many antiperspirants also contain antibacterial compounds that cut down the populations of some microorganisms. Sweat itself has been shown to contain an antimicrobial protein that might help regulate skin bacteria[4].

Deodorants combat body odor by using antibacterial compounds and/or odor-masking effects,

but they do not plug the sweat glands3. Natural deodorants can also have antibacterial and odor-masking effects. Many essential oils have strong antimicrobial effects as well as aromatic properties. Skin pH has a strong (and variable) effect on microorganisms. The typical pH of the armpit is reported as ~5.8 in men and ~6.0 in women, and maximum odor production seems to occur around that pH[5]. Growth of some common microbial pathogens is inhibited at acidic pH and enhanced at more neutral pH[6].

There is a large amount of anecdotal evidence that baking soda (sodium bicarbonate),

an alkaline substance (pH ~8.3 in 0.1N solution), strongly inhibits odors. A study performed in the 1940s[7] looked at the use of baking soda as a deodorant and proposed an explanation for its striking ability to deter BO. The author, a dermatologist, suggested that the sodium bicarbonate reacts with volatile fatty acids and forms mild-smelling compounds. This keeps the fatty acids from wafting away with their “disagreeable odors.” It also stands to reason that microbial growth might be reduced in the higher-pH environment created when baking soda is used in deodorant, if optimal bacterial growth occurs at neutral or slightly acidic pH.

So consider these things when you’re thinking about what products to use on your underarm ecosystem:

  • First, Having a personal aroma isn’t necessarily something to avoid. There is speculation that odor molecules in sweat act as communication signals about attractiveness (odors may increase or decrease perceptions of attractiveness) or compatibility, and that they may affect mood. Is that necessarily something to try to blot out or cover up?
  • Commercial deodorants are big business, and this business was launched around 1919 by an advertising campaign that promoted the idea that odors made women unattractive and that they weren’t aware “how much sweeter and daintier they would be if they were entirely free from [perspiration]”! And that women were “beautiful but dumb” if they weren’t aware how unattractive perspiration made them!! Woah!! Despite the offensiveness of these ads, many people eventually caved to the pressure or bought in to the ideas, which more and more people are coming back to question…
  • There is an environmental impact of the chemical cocktails and plastic containers used for commercial antiperspirants & deodorants. Mining and processing aluminum exacts a heavy environmental toll. Triclosan (an antibacterial classified as a pesticide) is often used in these products and is an environmental pollutant (see this post on a recent FDA ruling).
  • Realistically, many of us do want some help reducing BO for any number of reasons. Fortunately, there are simple, natural alternatives to commercial products. You can make your own deodorizer with a dilute solution of vinegar that you swab on your pits. Mix about 1 part apple cider vinegar with 4 parts water and apply with a cloth or cotton pad. There are many other simple recipes for homemade deodorant using baking soda, coconut oil and other oils and butters, cornstarch and essential oils. And if you don’t want to make your own, you can always try one of ours!

Maybe our smells don’t stink after all!

 

References

[1] Wilke K., Martin A., Terstegen L. and Biel S.S. 2007. A short history of sweat gland biology. International Journal of Cosmetic Science 29, 169–179.

[2] James A.G., Austin C.J., Cox D.S., Taylor D., and Calvert R. 2013. Microbiological and biochemical origins of human axillary odour. FEMS Microbiology Ecology 83:527–540

[3] Abrutyn E.S. 2016. Antiperspirants and Deodorants. Chapter 18 in Cosmetic Dermatology: Products and Procedures, 2nd Ed. John Wiley & Sons, Ltd.

[4] Schittek B., Hipfel R., Sauer B., Bauer J., Kalbacher H., Stevanovic S., Schirle M., Schroeder K., Blin N., Meier F., Rassner G. and Garbe C. 2001. Dermcidin: a novel human antibiotic peptide secreted by sweat glands. Nature Immunology 12:1133–1137.

[5] Stenzaly-Achtert S., Schölermann A., Schreiber J., Diec K.H., Rippke F. and Bielfeldt S. 2000. Axillary pH and influence of deodorants. Skin Research and Technology 6:87–91.

[6] Grice E.A. and Segre J.A. 2011. The skin microbiome. Nature Reviews Microbiology 9:244–253.

[7]Henderson Lamb J. 1946. Sodium bicarbonate – an excellent deodorant. Journal of Investigative Dermatology 7:131–133.

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