miraDry vs botulinum toxin for sweating:
destroy the gland, or quieten the signal

How does miraDry work, and how does botulinum toxin stop sweating?

Sweat glands in the underarm sit in a thin band at the junction of the dermis and the fat beneath it. miraDry is a handpiece that delivers microwave energy to that band. Microwaves at the frequency it uses are absorbed preferentially by water-rich tissue, the gland layer is heated enough to destroy it, and a cooling plate at the surface protects the skin above. Vacuum holds the skin against the plate so that the energy is delivered at a consistent depth. The two early clinical evaluations in Dermatologic Surgery, one open-label and one randomised against a sham, described reductions in measured sweat and in a severity score in treated underarms, with swelling, soreness, numbness and small nodules under the skin as the usual after-effects. The device is cleared in the United States for axillary hyperhidrosis, and later for underarm odour and hair reduction, because apocrine glands and hair follicles sit in the same layer.

Botulinum toxin does not touch the gland. It is injected in a grid of small doses across the sweating area of the underarm skin, mapped beforehand with a starch-iodine test where that is useful, and it blocks the release of acetylcholine, the chemical messenger that the nerve uses to switch the gland on. The gland is intact but silent. The randomised, double-blind BMJ trial that established the approach for bilateral primary axillary hyperhidrosis measured a reduction in sweat production that held for months, after which the nerve endings recover and sweating returns. The botulinum toxin glossary entry describes the molecule; the botulinum toxin page lists underarm sweating alongside the facial areas it is used for here.

How long does miraDry last compared with botulinum toxin, in words?

The difference is structural rather than a matter of degree. A sweat gland that has been destroyed by heat is not replaced, so the reduction miraDry achieves in the glands it reaches is described as lasting; it does not reach every gland, which is why some people have a second treatment, and the body's other sweat glands are unaffected, which is why overall temperature regulation is not. Botulinum toxin is reversible by design: the nerve endings sprout new terminals in time, the signal returns, and the injection is repeated when it does. Some people find the interval lengthens with repeated cycles, others do not, and no interval is promised here because it varies between people and with dose.

That reversibility cuts both ways. For someone who is unsure, who may be pregnant in the coming year, or whose sweating is seasonal, a treatment that wears off is a feature. For someone who has had toxin for years and is tired of repeating it, an energy-based reduction is the logical next rung on the ladder set out on the excessive sweating page: clinical-strength antiperspirants, iontophoresis, botulinum toxin, energy-based gland reduction, then systemic options. The comprehensive 2019 review of therapeutic options in the Journal of the American Academy of Dermatology places microwave thermolysis and botulinum toxin on that ladder in the same order.

“I will not destroy a gland before I know the sweat is the problem. Toxin answers that question first, and it answers it reversibly.”

Dr Sin YongOn the order of treatments for underarm sweating

What is the downtime and what are the risks of each?

miraDry is the heavier of the two on the day and in the period after. The underarm is numbed with local anaesthetic, the treatment itself is a sequence of placements across a template, and afterwards the area swells, aches and can feel numb or tingly where the superficial nerves have been heated. Small firm lumps under the skin, bruising and tenderness are common and settle gradually; numbness can take longer; less common effects reported in the literature include temporary weakness of the arm from heating near a nerve, blistering and, rarely, infection. Underarm hair in the treated area is reduced as a side effect, which some people welcome and some do not.

Botulinum toxin is lighter. The injections sting, there may be pinpoint bruising, and normal activity resumes the same day. The risks are those of any injection, infection and bruising, plus the specific ones: compensatory sweating elsewhere is reported by some people, and a dose placed too deep can weaken nearby muscle for a time, which is why the medicine is placed in the skin rather than beneath it. Neither treatment is offered for sweating that is generalised, new in adulthood or nocturnal until the cause has been looked for, and neither is given in pregnancy. Someone with a neuromuscular condition or taking medicines that affect nerve transmission is assessed before toxin is considered. The complication care page lists the signs after any treatment that need prompt review.

Who suits miraDry, and who suits botulinum toxin for sweating?

Botulinum toxin suits most people with confirmed primary axillary hyperhidrosis who have tried a clinical-strength antiperspirant properly, applied at night, and found it insufficient. It suits a first treatment because it is reversible and because the result tells both patient and doctor how much of the problem was sweat: if the shirts stay dry, the diagnosis is confirmed. It suits anyone who may be pregnant soon, whose sweating is tied to a season or a job, or who wants to keep their underarm hair and odour as they are. It does not suit someone unwilling to repeat a treatment, or whose main problem is odour rather than wetness, which is apocrine and is assessed separately.

miraDry suits someone with established primary axillary hyperhidrosis who has responded to toxin and wants a reduction that does not need repeating on a cycle, who can accept a period of a swollen, numb underarm, and who does not mind losing some underarm hair. It is an underarm treatment only, so palms, soles and facial sweating are not candidates. It does not suit someone whose diagnosis is uncertain, because destroying glands is not the right first test, or anyone whose sweating has not yet been assessed for a secondary cause. Dark underarms, odour and ingrown hairs often arrive in the same consultation as sweating; the dark underarms treatment page covers how those are separated and planned together.

The questions that sort it

• Is this primary focal hyperhidrosis, by history and pattern, or does the sweating need investigating first?
• Has a clinical-strength antiperspirant been used correctly, at night, on dry skin?
• Is reversibility a feature or a nuisance for this person?
• Is the complaint wetness, odour, pigment or hair, or several at once?

How does Dr Sin Yong treat underarm sweating, and why not miraDry?

Underarm sweating here is treated with botulinum toxin injection, placed by Dr Sin Yong after a clinical assessment that confirms primary focal hyperhidrosis and rules out the patterns that need investigation. miraDry is not used here. The toxin step sits in the middle of the ladder: a clinical-strength antiperspirant is confirmed to have been tried first, and someone who has done well on toxin for years and wants an energy-based gland reduction is told so and directed to where that is appropriate. What decides the plan is the diagnosis, the severity, the area, whether odour or pigment are part of the complaint, any medicines or conditions that bear on toxin, and how the person feels about repeating a treatment.

Aftercare after toxin for sweating is simple and is explained on the day: keep the area clean, avoid rubbing it or applying deodorant until the next day, and note when the sweating returns so that the interval is known for next time. The medicine is prescription-only in Singapore and is prescribed and injected by the doctor; nobody else places it here. Fees follow the dose and the areas and are set out in writing after assessment, as explained on how fees are quoted. The condition itself, how it is diagnosed and what does not work for it are covered on the excessive sweating page.