One armpit can smell worse than the other because the two sides have different bacteria, and different bacteria produce different smells. Some produce odor when they break down sweat compounds, while others break them down into odorless substances.

One-sided armpit odor is very common. I’ve spent 15 years researching body odor and sampling thousands of armpits, and around 50% of people smelled differently in their left versus right underarm. Below I explain why only one armpit smells and give you two things you can do about it.

What causes armpit odor?

Fresh sweat is odorless. What you smell is your armpit microbiome at work.

The bacteria that cause body odor eat the sweat and break it down into smelly compounds, and each species makes a different smell. Oniony body odor, for example, comes from Staphylococcus hominis breaking down certain molecules in sweat into volatile sulfurous thioalcohols (3M3SH). And sour and musty body odor come from Corynebacterium breaking precursors down into that specific scent.

What most people don’t know is that your underarms also host good bacteria that neutralize odor precursors in sweat. Staphylococcus epidermidis eats sweat and breaks it all the way down into carbon dioxide and water, which are odorless. Everyone has them already on their skin.

When your microbiome is dominated by these good bacteria, you don’t smell. When odor-producing species dominate, you do. So it’s a matter of finding the right balance.

Can the bacteria in each armpit be different?

One armpit smells worse because its microbiome is smellier, with more odor-producing species like Staphylococcus hominis and Corynebacterium.

There’s a distance between your two armpits, and that distance is enough for the bacteria on each side to end up very different, which is what creates uneven body odor. Your right armpit can carry the good microbiome that never causes malodors, dominated by Staphylococcus epidermidis. Your left can be dominated by Corynebacterium.

It can also be because one armpit produces more apocrine sweat and more precursors for body odor than the other. That in itself also leads to a differential underarm microbiome. 

Why does the same armpit keep smelling after a shower?

The odor-producing bacteria not only are present on the skin, but also in the sweat glands and the hair follicles, deeper in the skin. That’s the mother nests of the skin microbiome. Washing doesn’t reach them, and that’s why persistent armpit smell stays on the same side and why a shower doesn’t fix it.

It is however possible to change this. It just takes a thorough understanding of the science.

How can you get rid of odor in one armpit?

The goal is to shift the microbiome from one dominated by odor-producing species to one dominated by good ones like Staph epidermidis. In other words, you go from a smelly microbiome to a non-smelly one.

There are many ways to do that. If one armpit smells and the other doesn’t, these are two of the best things you can try.

Option 1: Try an armpit detox

Stop wearing deodorants and antiperspirants for two weeks.

Good bacteria like Staphylococcus epidermidis naturally live in our underarms. They even produce antimicrobial molecules that help keep odor-producing species in check.

Deodorants and antiperspirants can disrupt that balance. They kill the good bacteria, while more resistant odor-producing bacteria survive and take over. Gram-negative bacteria crop up after long-term use of antibacterial ingredients, and they cause the pungent bad odors.

Quitting these products gives your microbiome a chance to rebalance and gives the good bacteria an opportunity to take back control. The Gram-positive bacteria then have the chance to conquer the niche of the Gram-negative bacteria.

[LINK: full armpit detox post, coming soon] I’ll break down the full routine there.

Option 2: Lower the pH with lemon juice

Apply lemon juice daily for two weeks to the armpit that smells. You can rub it directly against the skin, or squeeze the juice and apply it with a cotton pad or a spray bottle.

It neutralizes the odor, inhibits the smelly bacteria, and creates an environment where the good bacteria can establish themselves. This works because the smelly bacteria prefer a higher pH, while the good ones prefer the skin’s naturally acidic pH. It’s very effective, and you should see improvements in under a week. Keep in mind that you shouldn’t sunbathe your armpits after applying it.

[LINK: full lemon juice post, coming soon] I’ll break down the whole routine there.

What does your non-smelly armpit tell you?