Body odour (bromhidrosis) in Singapore:
apocrine sweat, bacteria, and which treatments act on which

Apocrine vs eccrine sweat: why sweat does not smell until bacteria get to it

The skin carries two kinds of sweat gland and they do different jobs. Eccrine glands, several million of them, are spread over the whole body and open directly onto the surface. They produce the watery sweat that cools you, and it is almost odourless: water, salt and traces of urea and lactate. Apocrine glands are far fewer, are confined to the underarms, groin, around the nipples and the ear canal, open into hair follicles rather than onto the skin, and only begin to work at puberty under the influence of sex hormones. Their secretion is thick, milky and rich in lipids, proteins and sulphur-containing precursors, and it is also odourless as it leaves the gland.

The smell is made on the skin. Bacteria that live in the moist, hairy underarm, chiefly corynebacteria and some staphylococci, metabolise apocrine precursors into short volatile fatty acids with a rancid, cheese-like note and into thioalcohols with the sharp, sulphurous quality people describe as onion. Eccrine sweat does not supply the precursors, but it supplies the wet environment and dilutes the acidity of the skin, which lets the bacteria thrive, and underarm hair gives them more surface and holds the volatile products close. So apocrine bromhidrosis, the common form, needs three ingredients at once: apocrine secretion, bacteria and moisture. Take away any one and the odour falls.

Eccrine bromhidrosis is different and less common. It arises where eccrine sweat macerates the outer skin layer, usually on the feet or in skin folds, and bacteria then digest the softened keratin; the smell is more sour and the sites are different. It responds to keeping the area dry rather than to anything aimed at apocrine glands, which is one reason the site of the odour is the first thing asked about.

Why do some people have body odour and others almost none?

Apocrine activity varies enormously between people, and part of the variation is written in a single gene. A common variant of ABCC11 reduces the secretion of odour precursors by apocrine glands, and the same variant produces dry, flaky earwax instead of wet. It is carried by most people of East Asian ancestry and by a minority of Europeans and Africans, which is why axillary odour is reported far less often in Chinese, Japanese and Korean populations and why dry earwax and low odour so often go together. In Singapore's mixed population this matters clinically: in someone with dry earwax, a new complaint of strong underarm odour prompts a closer look at bacteria, skin folds, products and medical causes rather than at the glands.

Other things that raise odour are more ordinary. Dense underarm hair, synthetic fabrics that trap moisture, humidity, infrequent changes of clothing, diets heavy in garlic, onion, cruciferous vegetables or spices whose sulphur compounds are excreted in sweat, alcohol, stress and anxiety which drive apocrine as well as eccrine output, hormonal shifts at puberty, around periods, in pregnancy and at the menopause, and some medicines. Excessive eccrine sweating on its own, hyperhidrosis, does not smell, but it makes an odour that is already there worse by keeping the skin wet, and the two are often treated together.

Lookalikes in the underarm

• Erythrasma: a brown, slightly scaly patch in the fold caused by a corynebacterium, which fluoresces coral-red under a Wood's lamp and needs an antibacterial treatment, not deodorant.
• Trichomycosis axillaris: yellow, red or black concretions stuck to the hair shafts, with odour and stained clothing; shaving and an antibacterial clear it.
• Intertrigo and fungal infection of the fold: red, raw, sometimes with satellite spots; treated as infection.
• Hidradenitis: painful recurring boils and tunnels in the underarm or groin, with discharge; a dermatology referral, not an odour treatment.

“Sweat does not smell. Bacteria eating sweat smell. So before I inject anything I want to know you have starved them of hair and moisture for a month, and if your earwax is dry I want to know why you smell at all.”

Dr Sin YongOn body odour

The hygiene baseline: what to do before any procedure

Because odour needs bacteria and moisture, the baseline removes both, and for many people it is the whole answer. It is listed before the clinical options because Dr Sin Yong will not inject or treat an underarm that has not first been managed this way.

• Wash the right way. An antibacterial wash containing chlorhexidine or benzoyl peroxide, used on the underarms and groin daily, lowers the bacterial load that makes the smell. Ordinary soap removes sweat; it does little to the resident bacteria.
• Dry completely, then antiperspirant at night. An aluminium-based antiperspirant applied to dry skin at bedtime blocks eccrine ducts while they are quiet, and the block holds through the next day; applied in the morning on damp skin it does far less. A deodorant masks or acidifies; it does not reduce sweat.
• Remove the hair. Less hair means less surface for bacteria and less trapped odour. Shaving helps; laser hair removal of the underarm does the same without the daily irritation that also darkens the skin.
• Fabric and frequency. Cotton or moisture-wicking fabrics, a fresh shirt each day, and washing sportswear at a temperature that kills bacteria rather than a cool cycle that leaves them in the fibres.
• Topical antibacterials. A short course of a topical clindamycin or erythromycin preparation, prescribed after examination, can reset the bacterial population when the wash alone is not enough; it is not a long-term answer because resistance follows.
• Diet, where it is obvious. Reducing garlic, onion, strong spices and alcohol for two weeks is a reasonable test if the odour has a sharp, sulphurous quality.

If the odour persists after a genuine month of this, the problem is apocrine output or sweat volume, and the clinical options below are considered.

Botulinum toxin, microwave and laser for body odour: what each acts on

The clinical options act at different points in the chain, and it helps to know which before comparing them.

Botulinum toxin injection

Botulinum toxin injected into the skin of the underarm blocks the nerve signal that tells sweat glands to secrete. Its main and well-established use is for excessive eccrine sweating, and by drying the underarm it removes the moisture that bacteria need, which is why odour falls with it. There is also direct evidence for bromhidrosis: a 2019 randomised, double-blind, side-by-side trial found reduced odour scores on the treated side with histological changes in the sweat glands, and a 2024 review in Dermatologic Surgery covers its use for apocrine as well as eccrine gland disorders. The effect wears off and is repeated; the molecule is a prescription medicine placed by a doctor. This is the injectable rung Dr Sin Yong uses for sweat-driven odour, after the baseline has been tried, and the areas and technique are described on the botulinum toxin page.

Microwave gland reduction

A microwave device delivers energy to the junction of the dermis and fat where both eccrine and apocrine glands sit, and destroys them by heat with surface cooling. It was developed for axillary hyperhidrosis and has been studied for bromhidrosis, with 2025 histological work in Dermatologic Surgery showing apocrine gland changes. Because destroyed glands are not replaced, it is described as lasting, with swelling, numbness and tenderness afterwards that settle gradually. It is not used at this practice; the comparison with toxin is on miraDry vs botulinum toxin.

Laser and surgical gland removal

Subdermal laser, using a fibre passed under the skin of the underarm to heat the gland layer, and suction-curettage or open excision of the apocrine tissue are described in the surgical literature, mostly from East Asia where apocrine bromhidrosis in a person without the protective gene variant can be severe. They carry the risks of any procedure under the skin, including seroma, scarring, skin necrosis and recurrence, and they are plastic surgery or dermatological surgery procedures, not offered here. A 2023 literature review in the Journal of the American Academy of Dermatology sets out all these modalities side by side.

When body odour is medical, and goes to a GP first

Most bromhidrosis is local and harmless. A minority of odour complaints are the first sign of something else, and these are referred rather than treated.

• Whole-body odour or a change in your usual smell. Liver and kidney disease, uncontrolled diabetes, with its sweet or acetone note, and thyroid overactivity change the chemistry of sweat and breath. Odour with thirst, weight loss, fever or fatigue is a GP visit with blood tests.
• A fishy odour of sweat, breath and urine, worse after fish, eggs or beans, may be trimethylaminuria, a metabolic condition diagnosed by a urine test and managed by diet; it is not an underarm problem.
• Odour from a rash, a fold, a wound or a discharge is infection until proven otherwise: intertrigo, erythrasma, a fungal infection, hidradenitis or an infected cyst, each treated as such.
• Medicines including some antidepressants, antipyretics and supplements change sweat composition; a pharmacist or GP review comes before any procedure.
• Odour that others cannot detect. Some people are convinced of a smell that family, colleagues and the examining doctor cannot perceive. This is a recognised and distressing condition in its own right, and it is taken seriously; what it needs is a GP conversation rather than repeated procedures on the underarm, and Dr Sin Yong will say so kindly and plainly if that is what he finds.

What decides the plan, and aftercare

For odour that is genuinely apocrine and local, what decides the plan is the site, the contribution of eccrine sweating, hair density, skin phototype where laser hair removal is part of it, the response to a proper baseline, and your tolerance for a treatment that is repeated. After botulinum toxin injection, expect small bumps and occasional bruises that settle, no pressure on the area that day, and a review before any repeat; after laser hair removal, the usual sun avoidance and bland care described in the aftercare hub. The fee follows what is chosen and is set out in writing after the consultation.