Sweat glands sit at the boundary between the skin and the fat underneath. Microwave energy is drawn to water, and sweat glands are the wettest thing in that layer, so the energy concentrates there and heats them until they are destroyed. At the same time, the handpiece cools the surface of the skin, which is what stops the top layers from burning while the deeper layer cooks.
Sweat glands do not regenerate. Once they are gone from a treated patch of underarm, they are gone. That is why the result is described as permanent, and it is a genuinely different proposition from botulinum toxin, which blocks the nerve signal to glands that are still there and wears off.
The same layer holds the apocrine glands, which are the source of underarm odor, and the hair follicles. So miraDry usually reduces smell and hair as well. For some people the odor change matters more than the sweat change.
One thing it cannot do is treat anywhere else. The device is designed and cleared for the underarm. Palms, soles, face and groin are not treated with it — the anatomy underneath is different and the nerve and structure risks are not acceptable.
Get the diagnosis straight first. If your sweating started suddenly, affects one side, or comes with fevers, weight loss or night sweats, that needs investigating before you treat it.
Ask the clinic how many miraDry treatments they have actually done. This is a procedure where careful mapping and adequate numbing make a large difference to both comfort and result, and it is done less often than it used to be. If nobody local offers it, that is worth knowing before you build your plans around it.
Ask directly what the price covers — one session or the standard two. Packages differ and a single-session quote can look misleadingly cheap.
Stop shaving pressure aside, most clinics ask you to let underarm hair grow to a few days' length or to shave a few days before, because the hair pattern is used for mapping. Follow their specific instruction.
Wear a top you can take off and put back on easily, and expect to be there for one to two hours, most of which is numbing.
Take a dose of a plain pain reliever beforehand if your clinic suggests it. Numbing is by injection and there is a lot of it.
Arrange a ride if you are anxious about needles or your clinic offers a sedative. Otherwise you can drive yourself home.
A temporary tattoo-style grid is stamped onto each underarm. That grid is how the provider makes sure the whole sweating area is covered without treating the same spot twice.
The provider injects local anesthetic across the whole underarm. This is the uncomfortable part and there is no way around it — a properly numbed underarm takes many injections. It usually takes longer than the treatment itself.
Once numb, the handpiece is placed on each square of the grid in turn. It suctions the skin up into the tip, so the sweat gland layer is pulled closer to the energy and the deeper tissue is pulled away from it. You hear it start and feel a pulling sensation.
Each placement takes under a minute. The device fires while the surface is cooled. You may feel warmth or a mild ache but should not feel burning. Say so if you do.
The whole grid is worked through, then the other side. Treatment time is typically 20 to 40 minutes per underarm.
Ice packs go on afterward and you go home the same day.
The first few days are the worst of it. Both underarms are swollen, tender and often quite firm. Some people describe it as looking like they are hiding something under each arm.
Ice and a plain anti-inflammatory like ibuprofen handle most of the discomfort. Many clinics recommend icing on and off for the first 24 to 48 hours.
Raising your arms fully overhead is uncomfortable for several days. People typically go back to desk work the next day and skip the gym for a week.
Firm lumps and cords under the arm are normal and are the single most common surprise. They can persist for several weeks to a couple of months and gradually soften. Gentle massage helps.
Numbness or a patch of odd sensation in the underarm or on the inner upper arm is common and almost always temporary, though it can take weeks to months to fully settle.
Underarm hair thins or falls out in the treated area over the following weeks. Plan for that rather than being surprised by it.
Most people get a large reduction in underarm sweating that they can feel within days and that improves further over the first few months.
Most people need two sessions to be satisfied. The second one treats what the first missed and the gap between them is usually about three months. Being underwhelmed after one session is normal and is not a sign it failed.
Reduction, not elimination. The realistic outcome is going from soaking shirts to normal-feeling underarms — not to bone-dry skin. Some sweating remains, and that is expected; the underarm still needs to be able to sweat a little.
Odor usually improves along with the sweat, and for a subset of people that is the more valuable half of the result.
How long it lasts: destroyed glands do not come back, so the results hold for years. A small number of people notice some sweating creep back and choose a touch-up. Follow-up data stretching out a decade or more is thinner than the word "permanent" implies, so treat it as long-lasting rather than guaranteed for life.
Who is disappointed: people who expected zero sweat, people whose sweating was never mostly in the underarms, and people who only had one session and stopped there.
There is no home version. miraDry is a medical microwave device, it is not sold to consumers, and the numbing alone puts it out of reach of home use.
What does exist at home is the whole first tier of hyperhidrosis care, and it is worth exhausting before spending thousands. Clinical-strength aluminum chloride antiperspirants applied at night to completely dry skin help a lot of people who assumed antiperspirant "does not work" because they were using it wrong. Prescription wipes like Qbrexza and Sofdra are applied at home. Iontophoresis can be done at home with your own machine, though it is awkward in the underarm.
Beware of home microwave, radiofrequency or "sweat gland zapping" gadgets sold online. Nothing sold direct to consumers delivers controlled energy to that depth with surface cooling, and heating your own underarm without either is a good way to get a burn.