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The Nose Knows: The Microbiome and Body Odor

Our bodies are home to many microbial communities, some that produce smells we love – like the top of a baby’s head, or a loved one’s unique scent – and some that can cause bad odors when bacterial populations are thrown off balance. The distinctive smell of morning breath, for example, occurs when we sleep with our mouths closed and breathe primarily through our noses. Lower levels of oxygen in the mouth increase the numbers of anaerobic bacteria during the night, and their waste products give our breath a sour smell.

Most animals, in fact, can detect variations in each others’ microbiomes. Animals use scent to recognize each other, detect fear in their prey, and know when females are in heat.

As a gastroenterologist, the body’s odors clue me in to a patient’s health issues. People who have inflammation in their colon from Crohn’s disease, ulcerative colitis, or an acute infection experience significant shifts in the composition of their gut bacteria—changes that I can smell even before I insert a scope to examine the colon.

Body odors are not always a sign of bad health. In fact, the products we use to cover up our normal smells can worsen our health.

For example, we spend a lot of money on products to eliminate underarm odor. However, a Belgian study confirmed what I have long suspected: the more antiperspirant you use, the more you need.

There are the two main types of bacteria that inhabit your armpits: Staphylococci and Corynebacterium. Staph tends to be the dominant species in women and has very little smell. The more odor-producing Corynebacterium is predominant in men, probably because they secrete more fat in their sweat, which is the preferred food of the lipid-loving Corynebacterium.

Aluminum salts in antiperspirants have a considerable impact on Staph, depleting their numbers, which leads to an increase in the population of smelly Corynebacterium. When you use these products, you’re actually altering the microbiome of your armpit, and not for the better.

Vaginal douching is a similarly bad idea. It not only begets more douching but also decreases the native protective Lactobacillus population and increases the risk of sexually transmitted diseases and urinary tract infections.

If quitting antiperspirants cold turkey seems too drastic, consider using less or going without on days when you’re not working closely with others. You can also dab a few drops of lavender essential oil under your armpits. Pungent bacteria from your skin grow more readily on synthetic fabrics such as polyester, so wearing clothes made from natural fabrics like cotton or linen can also help with odor control.

Attitudes toward body odor vary across cultures, and it might be helpful to follow the lead of societies where there’s more acceptance for personal odors. It may take some getting used to, but noses do acclimate to our more natural smells.

Chilling out and changing your diet can also help you smell better. You have two kinds of sweat glands: eccrine glands, which are located all over your body and open to the skin, and apocrine glands, which release their contents into areas with hair follicles, like your armpits and groin. Eccrine glands secrete odorless water and salt onto your skin when it’s hot or when you’re exercising, which helps cool you off as it evaporates. Apocrine glands release a milky white substance when you’re stressed that combines with bacteria in your armpits and groin to create a smelly body odor.

Most people can clearly distinguish between the slightly salty smell they have after a hard workout or hot day and the mustier smell of being stressed out—all the more reason to hone your relaxation response!

Stress can make us smelly, and so can our diet. We’re not alone in this: cows that are fed corn on the feedlot tend to have malodorous stool and gas since an unnatural diet like corn (instead of grass) promotes the growth of more pathogenic microbes in their gut, like E. coli.

We suffer the same misfortune when it comes to our own body odor, stool, and gas when we eat an unnatural diet full of processed meats and grains instead of fresh fruits and vegetables. In fact, a study published in Chemical Senses found that women rated male body odor as more “attractive and pleasant” when the men abstained from meat for two weeks.

If you’re looking to restore your gut bacteria to a more balanced state, focus on a plant-based, whole food diet, rich in leafy greens and indigestible plant fiber. A change in your personal aroma is one of the first things you’ll notice as your microbiome becomes healthier.

The nose knows!

Dr. Robynne Chutkan is an integrative gastroenterologist and the author of Gutbliss, The Microbiome Solution, and The Bloat Cure. Educated at Yale and Columbia, she has served on the faculty at Georgetown University Hospital since 1997 and is the founder of the Digestive Center for Wellness, an integrative gastroenterology practice incorporating microbiome analysis, nutritional counseling, and biofeedback as part of the therapeutic approach to digestive disorders. An avid runner, snowboarder, and yogi, she is passionate about helping her patients live not just longer lives, but dirtier ones! Connect with her on Facebook, Instagram, and Twitter.