Strong Underarm Odour Even After Bathing? Dermatologist Explains Why Armpits Smell May Return

Strong underarm odour can be a real issue of embarrassment, particularly when it re-occurs shortly after showering. Many people think that it just means that they sweat too much or don't clean their armpits enough. However, the odor may not be attributed solely to the sweat. 

The odour comes from the release of some of these substances by apocrine sweat glands and the activity of bacteria that reside on the skin. It can be the reason for some people smelling foul despite taking a bath. That is, armpits is not necessarily a hygiene concern.

Is Underarm Odour Actually Caused By Sweat?

Dr Chandni Jain Gupta, Dermatologist, Elantis Healthcare, Lajpat Nagar explains, “It's not sweat itself, and that's the key thing most people get wrong. Fresh apocrine sweat, the thick secretion your armpits produce, is essentially odourless when it first reaches the skin. The smell you're actually noticing is the byproduct of specific skin bacteria breaking that sweat down into volatile compounds.”

While bathing removes sweat and bacteria from the surface of the skin, it does not affect the amount of odour-precursor that the glands release, or the efficiency of an individual's bacterial population in converting it, she adds.

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This implies that when someone bathes, odour may come back even if the person washes well.

What Happens In Your Armpits To Produce The Smell?

There are two main types of sweat glands in the armpits.

• Eccrine glands produce watery sweat that helps cool the body.
• Apocrine glands produce a thicker secretion and are concentrated in areas such as the armpits and groin. They become active after puberty.
• The apocrine secretion itself is odourless. The characteristic smell develops when certain skin bacteria break down compounds in this secretion.
• One of the bacteria involved is Staphylococcus hominis. It can convert sweat-derived compounds into sulphur-containing molecules called thioalcohols, which contribute to typical underarm odour.

A 2024 study published in the Journal of Biological Chemistry investigated one of the biochemical steps involved in producing human body odour. During the pathway that leads to the formation of an odour precursor called 3-methyl-3-sulfanylhexan-1-ol (3M6H), researchers identified an enzyme that is produced by Staphylococcus hominis and helps to break down the odour precursor.

This is crucial as it gives more specific evidence that body odour isn't just caused by sweat on the skin. Certain bacteria and enzymes are responsible for the transformation of otherwise non-odourless compounds into volatile compounds that are detectable by the nose.

Why Can Underarm Odour Return Soon After Bathing?

A shower removes sweat, bacteria and residue that are already present on the skin. But it does not permanently alter the underlying processes that contribute to odour.

Dr Gupta explains that two factors matter particularly:

• How much odour-precursor material the apocrine glands release
• How quickly the person's skin bacteria regenerate and begin converting those compounds again

For some people, this process can restart relatively quickly. That is why strong odour may become noticeable again within hours of bathing.

So, frequent washing is not necessarily the complete answer when the underlying production of odour precursors and their bacterial conversion remains unchanged.

Can Genetics Affect How Much You Smell?

Yes. Dr Gupta explains that genetics can have a significant role.

A gene called ABCC11 affects how much odour-precursor material is transported into apocrine secretions. Certain variants of this gene are associated with reduced production of the compounds that odour-causing bacteria use.

The same genetic variation is also associated with dry, flaky earwax rather than wet earwax. This is why earwax type has been studied as an informal clue when researchers look at this genetic pathway.

A 2024 study in Scientific Reports examined the relationship between gene variants of ABCC11 and the bacteria within the armpit microbiome. Particular ABCC11 variants were associated with the presence of genes from bacteria that are important for the biosynthesis of 3M3SH and thus for axillary odour. Additionally, the study revealed that the ABCC11 variant accounted for some of the variation in the axillary microbiome.

The results indicate that genes and the skin microbiome may interact in the control of underarm odor. But this doesn't mean that everyone with this will have a noticeable body odor.

Why Do Some People Have Strong Odour Despite Good Hygiene?

According to Dr Gupta, several factors can contribute:

• A naturally higher concentration of bacteria involved in odour production
• Genetic differences affecting apocrine secretions
• Hormonal changes during puberty or menstrual cycle fluctuations
• Certain hormonal conditions
• Foods such as garlic, spices and red meat, which can influence sweat composition
• Excess underarm hair, which can provide more surface area for bacteria and trap sweat and bacterial byproducts
• Axillary osmidrosis, a rare condition involving excessive and often hereditary production of apocrine odour

This is why strong body odour does not automatically mean someone has poor personal hygiene.

What Can Actually Help Reduce Strong Underarm Odour?

Dr Gupta suggests methods to either promote sweating or the bacteria that cause the odours.

Antiperspirants

Anti-perspirants can help keep sweat from reaching the skin. This results in reduced raw material for bacteria to turn into odour causing substances.

Targeted washes

Washing with antibacterial or benzoyl peroxide under the arm could help lower the particular bacteria that causes the odour.

Remove hair from underarm area

Shaving or trimming may decrease the surface area available for bacterial growth, and may also be able to lessen the quantity of sweat and associated bacteria trapped around the hair.

Change sweaty clothes

Quickly changing into clean clothes after being drenched in sweat can minimize extended contact with wet clothes, sweat and germs.

If the sweating is persistent or severe, a dermatologist might consider discussing clinical strength antiperspirants, botulinum toxin injections to help decrease sweat gland activity or procedures for the confirmed axillary osmidrosis.

When Should Strong Underarm Odour Be Checked By A Dermatologist?

Consider medical evaluation if:

• The odour seems unusually strong compared with the amount of sweating.
• It continues despite thorough hygiene and regular antiperspirant use.
• A strong smell returns very soon after bathing, particularly if it appears to run in the family.
• Sweating is excessive enough to regularly soak through clothing.
• The odour is accompanied by a rash, irritation or discomfort.

Dr Gupta says these situations may need more than a stronger deodorant. Excessive sweating may require assessment for hyperhidrosis, while persistent strong odour may need evaluation for conditions such as axillary osmidrosis.

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Conclusion

If you are having a very strong underarm odor after bathing, this does not necessarily mean that you are not bathing properly. The apocrine sweat glands produce sweat that, when it gets to the skin, is relatively odorless. The odour is formed as a result of changes in the chemical composition of the skin by bacteria.

All of these can affect this process, including genetics, skin microbiome, hormones, diet and sweating. If the odor persists despite proper hygiene, it could be due to the actions that are taken after perspiration gets into contact with the skin, and not just how often you bathe.