In short. How toxin treatment works in the underarm, how long the effect lasts, why it needs repeating, and the question of compensatory sweating.
Key points
- The procedure is a series of small injections across an area that has been mapped out beforehand, usually after a starch-iodine test to show where the sweating actually is.
- It takes a short appointment, needs no anaesthetic for the underarm, and normal activity can be resumed the same day.
In axillary hyperhidrosis the sweat glands themselves are normal. The problem lies with the sympathetic nerve endings that tell the glands to produce sweat: they release a chemical transmitter, and the gland responds. Botulinum toxin type A is injected into the skin of the underarm, where it blocks the release of that transmitter from those nerve endings, so the gland stops receiving the instruction to sweat.
Nothing is destroyed. The gland is not removed and the nerve ending is not permanently damaged. The block wears off as the nerve terminal regrows, and that is exactly why the effect is temporary.
What it achieves
It is the best-evidenced treatment for underarm sweating. Most people get a large reduction, and many reach a point where they no longer think about their underarms from day to day. The sweat that remains is usually much reduced. It does not work for everyone, and a small number of people get little from it.
What the appointment involves
The procedure is a series of small injections across an area that has been mapped out beforehand, usually after a starch-iodine test to show where the sweating actually is. It takes a short appointment, needs no anaesthetic for the underarm, and normal activity can be resumed the same day.
How long it lasts
The effect usually begins within about a week, is at its fullest in the first weeks, and lasts on average somewhere between four and seven months. Sweating then returns to its previous level — not worse than before. Treatment is therefore repeated, usually a few times a year, and the interval is decided for each person rather than fixed in advance. This is a temporary treatment that has to be repeated to keep working, and it is not a cure.
Side effects and limits
Discomfort and bruising at the injection sites are common and settle. Occasionally there is a brief flu-like feeling. Very rarely there is a more generalised weakness that requires medical review. It is not equally effective at every site, it requires repeat visits and ongoing cost, and it does not suit everyone.
Compensatory sweating
This is the question people ask most, and it deserves an answer before treatment rather than after. When one area stops sweating, the body may compensate somewhere else, and a proportion of people notice more sweating on the back, the abdomen or the thighs. It is usually mild and often settles over time, but it is real, and it is not predictable for any individual.
Ask these before you decide
- How much of my sweating is likely to remain after treatment?
- What will be done if compensatory sweating appears elsewhere?
- How often will I need to return, and what will that cost over a year?
Frequently asked questions
How long does botulinum toxin last in the underarm?
The effect usually begins within about a week, is at its fullest in the first weeks, and lasts on average somewhere between four and seven months. Sweating then returns to its previous level, not worse than before, so treatment is repeated, usually a few times a year.
Does the injection destroy the sweat glands?
No. The toxin blocks the release of the chemical transmitter from the sympathetic nerve endings, so the gland stops receiving the instruction to sweat. Neither the gland nor the nerve ending is permanently destroyed. The block wears off as the nerve terminal regrows, which is exactly why the effect is temporary.
What is compensatory sweating, and will I get it?
When one area stops sweating the body may compensate somewhere else, and a proportion of people notice more sweating on the back, the abdomen or the thighs. It is usually mild and often settles over time, but it is real and it is not predictable for any individual.
Risks & Limitations
- Antiperspirants and topical agents commonly cause stinging, redness, dryness and irritation, and occasionally an allergic rash that requires stopping the product.
- Oral anticholinergic treatment can cause dry mouth, blurred vision, constipation and urinary symptoms, and cognitive effects are a particular concern in older adults.
- Botulinum toxin for palmar sweating carries a real risk of temporary weakness of the small muscles of the hand, which recovers but can interfere with work and driving.
- Botulinum toxin treatment is temporary, lasting months rather than permanently, and must be repeated to keep working.
- Compensatory sweating — new sweating appearing elsewhere — can follow any treatment that stops sweating in one area.
- After sympathectomy, compensatory sweating is common, often permanent, and cannot be undone reliably.
- No treatment is curative for everyone, and response cannot be predicted with certainty.
When to Seek Care
- Night sweats, especially with unexplained weight loss, fever or drenching, need medical assessment.
- Sweating with chest pain, palpitations, breathlessness or fainting — seek urgent medical care.
- Sweating that is one-sided or clearly asymmetrical, or that starts suddenly in later life.
- Sweating with heat intolerance, tremor, a swelling in the neck, or a change in menstrual pattern.
- Skin that is red, cracked, macerated, weeping or infected, or a rash that follows a new product.
- Urinary difficulty, confusion or drowsiness while taking oral treatment for sweating.
References & Further Reading
- American Academy of Dermatology (AAD) — public and clinical guidance on hyperhidrosis
- International Hyperhidrosis Society — patient and clinician resources on excessive sweating
- Chinese Medical Association, Dermatology Branch — clinical guidance
- Cochrane Library — systematic reviews of interventions for hyperhidrosis
- National Institute for Health and Care Excellence (NICE) — guidance on the management of primary hyperhidrosis
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.