Why Do My Armpits Smell Like Onions? (And How to Fix It)

The Sweat DeskBody odor

Quick answer: Armpits smell like onions because of sulfur compounds called thioalcohols. A skin bacterium, Staphylococcus hominis, makes them by breaking down odorless sweat from your apocrine glands. Stress, diet, and hormone changes can make the smell stronger. To cut it down, wash with an antibacterial or benzoyl peroxide wash, apply antiperspirant at night, and use a strong odor-control deodorant in the morning. If the smell changes suddenly or nothing helps, see a doctor.

If you’ve ever caught a whiff of something that smells like chopped onions and realized it was coming from your own armpits, you’re not alone. It’s a surprisingly common complaint, and there’s a clear scientific reason behind it.

This article explains where the smell comes from, what makes it worse, and the routine that helps most.

Infographic explaining why armpits smell like onions: odorless sweat is broken down by skin bacteria into onion-like thioalcohols, common triggers (stress, diet, hormones), four ways to cut the smell, and when to talk to a doctor. — The onion smell comes from sulfur compounds that skin bacteria make from sweat.

Why armpit odor can smell like onions

Fresh sweat has almost no smell. Your armpits have apocrine sweat glands, which release a thicker sweat that contains odorless compounds. Bacteria living on your skin break those compounds down, and that’s what creates body odor.

In 2020, researchers from the University of York and Unilever identified one of the key culprits. Their study, published in Scientific Reports, found that the bacterium Staphylococcus hominis uses an enzyme to turn an odorless sweat compound into thioalcohols, sulfur compounds with a strong smell. York microbiologist Dr. Gavin Thomas described their scent as onion-like.

That’s why the smell can seem so specific. Onions and garlic get their sharp smell from sulfur compounds too.

What makes the onion smell stronger

Stress

Stress sweat comes from apocrine glands, the same glands that feed odor-causing bacteria. That’s why a tense meeting or a nervous day can leave you smelling stronger than a workout. Board-certified dermatologist Dr. Azadeh Shirazi notes that higher cortisol levels from stress can change body odor.

Diet

Dr. Shirazi says garlic, onions, and spices can affect body odor. Red meat, cruciferous vegetables like broccoli and cabbage, asparagus, fish, and alcohol are also linked to stronger smells. If you notice the onion smell after certain meals, cutting back on those foods may help.

Hormones

Shifts during the menstrual cycle, pregnancy, and menopause can all change body odor. “With a decline in estrogen during menopause, higher levels of testosterone dominate,” Dr. Shirazi explains. Our menopause deodorant guide covers this in more detail.

Bromhidrosis

Some people have bromhidrosis, a condition where bacteria break down sweat into a strong sulfur- or onion-like smell. Dr. Shirazi says this odor “is more powerful than ordinary sweat.” If regular products don’t help, a dermatologist can confirm it and suggest treatment.

How to get rid of the onion smell

Wash to reduce bacteria. Use an antibacterial or benzoyl peroxide wash, and lather your underarms for at least 30 seconds, as Dr. Shirazi suggests. Our guide to the best soap for body odor covers the options.
Apply antiperspirant at night. Less sweat means less for odor bacteria to break down. Applying to dry skin before bed gives it time to work. See why nighttime application works.
Use deodorant in the morning. A strong odor-control formula handles what’s left. Dr. Shirazi often recommends a glycolic acid product a few times a week, since acids lower skin pH and make it less friendly to odor bacteria.
Mind your clothes and habits. Wear loose, breathable cotton, wash workout clothes promptly, keep underarm hair short, and manage stress where you can.

For the complete routine, see how to get rid of armpit odor. If your deodorant used to work and suddenly doesn’t, see why your deodorant stopped working.

When to see a doctor

Your body odor changes suddenly or strongly without a clear reason.
Over-the-counter washes, antiperspirants, and deodorants don’t control the smell. Dr. Shirazi says that’s the point to see a doctor.
You’re also sweating much more than usual. Dr. Shirazi notes that excessive sweating can sometimes point to conditions such as diabetes or an overactive thyroid.
For severe sweating, a dermatologist can discuss prescription-strength antiperspirants or Botox injections.

Products to try

Affiliate disclosure: Best for Deodorant may earn a commission when you buy through links on this page, at no additional cost to you. As an Amazon Associate, we earn from qualifying purchases. Read our full affiliate disclosure.

These picks from our buyer’s guides match each step of the routine above. For more options, see the best deodorant for body odor.

Step 1 · Wash
PanOxyl Acne Foaming Wash, 10% Benzoyl Peroxide

Type
Benzoyl peroxide wash
Note
Bleaches dyed fabric
Check price on Amazon
Step 2 · Night
Secret Clinical Strength Invisible Solid

Type
Clinical antiperspirant
Active
Aluminum zirconium 20%
Check price on Amazon
Step 3 · Morning
Lume Whole Body Solid Stick, Unscented

Type
Aluminum-free deodorant
Odor fighter
Mandelic acid
Check price on Amazon

Active ingredients come from each product’s label or brand page at the time of writing. Formulas change, so check the package you receive.

Frequently asked questions

Why do my armpits smell like onions?

Skin bacteria, especially Staphylococcus hominis, break down odorless compounds in apocrine sweat into sulfur compounds called thioalcohols. Researchers at the University of York describe their smell as onion-like. Stress, diet, and hormone changes can make it stronger.

Does eating onions make your armpits smell?

It can contribute. Dermatologists say garlic, onions, and spices can affect body odor. But the main cause of an onion smell is usually bacteria breaking down sweat, not your last meal, so washing and antiperspirant tend to help more than diet changes alone.

Why do my armpits smell like onions even after I shower?

Odor bacteria return quickly, especially if you sweat soon after showering. Regular soap may not reduce them enough. Lathering with an antibacterial or benzoyl peroxide wash for at least 30 seconds, drying fully, and applying antiperspirant at night usually helps. Clothes can also hold onto odor, so wash them promptly.

Can stress make my armpits smell like onions?

Yes. Stress sweat comes from apocrine glands, the same glands that produce the sweat odor bacteria feed on. That’s why stressful days can bring on a stronger, more oniony smell than heat or exercise.

Is an onion smell a sign of a health problem?

Usually not. It’s most often normal body odor from bacteria and sweat. But if your body odor changes suddenly, doesn’t respond to over-the-counter products, or comes with much heavier sweating than usual, talk to a doctor to rule out an underlying condition.

This article is educational and is not medical advice. If your body odor changes suddenly or doesn’t improve, talk to a doctor. Sources: University of York and Unilever study, Scientific Reports (2020), summarized by GIGAZINE; theSkimm, with board-certified dermatologist Dr. Azadeh Shirazi.

Why Do My Armpits Smell Like Onions?