Why does my underarm smell like onions?

Why does my underarm smell?

Underarms contain apocrine glands, a type of sweat gland that becomes active at puberty. Their secretions start out odourless. Bacteria break them down into substances including volatile acids, which produce the smell. Bacteria also break down skin oils and keratin, the protein in the outer skin layer. Persistent unpleasant body odour is called bromhidrosis.23

You can have strong underarm odour without noticeably wet armpits. The type of bacteria and its interaction with sweat matter, not just the amount of sweat. Sweating helps cool your body, and more sweating is normal during exercise, hot weather or anxiety.14

What can make the smell stronger?

Exercise, heat, stress and hormonal changes can affect body odour. Menopause can increase sweating. Foods such as onions, garlic and curry, along with alcohol, can contribute too. If the smell follows particular meals, try reducing those foods and watch whether the odour improves rather than cutting out everything at once.1

Medicines, including some antidepressants, and skin infections can also contribute. If a change began after starting a prescription and comes with excessive sweating, discuss it with the prescriber. Treatment can include changing the medicine with that doctor's help or treating the condition responsible.356

How to reduce the onion smell

1. 1Wash your underarms with soap at least twice a day, then dry them thoroughly.
2. 2Apply an antiperspirant to dry underarms before bed and let it dry completely. Follow the product's directions.
3. 3Change out of sweaty clothing promptly and wash clothes regularly. Choose loose cotton clothing rather than tight clothing.
4. 4If ordinary products are not enough, ask a pharmacist about stronger antiperspirants or a soap substitute that is gentler on your skin.

Underarm odour can cling to clothing, so a sweaty shirt can keep the smell going after your skin is clean, an unusually committed piece of laundry.3

Should you use deodorant or antiperspirant?

Deodorant masks odour with fragrance, which changes the scent rather than retiring the sweat glands. Antiperspirant reduces sweat production. Check that the packaging actually says "antiperspirant" if reducing wetness is your aim. Shaving underarm hair can also help control odour, although the benefit is uncertain.12

For diagnosed excessive sweating, bedtime antiperspirant treatment usually brings sweating under control within a few weeks. Maintenance use is often once or twice a week, depending on the treatment plan. That is a sweating timeline, not a deadline for the onion smell to disappear. Some persistent body odour cannot be completely suppressed.36

Antiperspirants can cause irritation or underarm discolouration. If either develops, tell your dermatologist rather than continuing the same routine unchanged. Longer gaps between applications, a different formula and making sure the skin is completely dry can help with irritation.6

When should you see a doctor?

Book an appointment if self care has not helped and the smell affects your confidence, changes from your usual odour, or comes with suddenly increased sweating. A new smell unrelated to washing habits also deserves assessment, especially if it affects your breath or urine as well. The doctor can check for infection, medicine effects or an underlying condition and offer treatment matched to the cause.135