Excessive Sweating: What Causes It? A Dermatologist Explains When to Look for a Cause, and Every Step of Treatment
Excessive sweating (hyperhidrosis) is not just "running hotter than other people." It is a condition in which the sweat glands work more than the body needs, to the point that it affects daily life: the embarrassment of a handshake, paperwork so damp you cannot write, shirts stained through so you carry a spare. Many patients live with it for ten years or more because they assume it is just how their body is and cannot be fixed. In truth, it can be treated, and there are more options than most people think. In this article, a dermatologist explains what counts as abnormal, which patterns call for finding a cause quickly, and the treatment ladder from the simplest step to permanent options.
How much sweating counts as "abnormally excessive"?
Doctors do not use the amount of sweat as the measure; they look at the pattern. The commonly used criteria are excessive sweating beyond what the body needs, continuing for at least 6 months, together with at least 2 of these features:
Occurs on both sides about equally and fairly symmetrically
Happens at least once a week
Interferes with daily activities or work
Began before age 25
A family member has the same problem
Stops during sleep
The last point matters a great deal: the common type of excessive sweating "rests" during sleep. If you wake up with damp bedding, that is a different matter and another cause needs to be looked for.
There are 2 types of excessive sweating, and the second is the one that needs a cause found quickly
Primary focal hyperhidrosis, the most common type
It is not caused by another disease. It is a problem with how signals travel through the autonomic nervous system to the sweat glands. The glands themselves are normal; they are simply told to work too much. It usually starts in the teenage years or childhood, occurs in specific areas (palms, soles, underarms, face) on both sides, often runs in families, and stops during sleep. This group is not dangerous to the body but has a major impact on quality of life.
Secondary hyperhidrosis, with an underlying disease or medicine
It is caused by another condition that makes the whole body produce more sweat. Causes include an overactive thyroid, diabetes and low blood sugar, menopause, chronic infections such as tuberculosis, some cancers (especially lymphoma), disorders of the pituitary and adrenal glands, severe anxiety, and many groups of medicines, such as SSRI antidepressants, opioid painkillers, and some fever reducers.
⚠️ Signs that it is not ordinary excessive sweating
If you have any of the following, see a doctor to look for the cause first, rather than focusing only on treating the sweating:
Onset after age 25 with no previous history
Sweating all over the body, not limited to the palms, soles, or underarms
Night sweats soaking the bedding
Sweating on one side only or asymmetrically, which may point to a nervous system problem
Other symptoms such as unintentional weight loss, persistent fever, palpitations, hand tremor, swollen lymph nodes, or unusual fatigue
Recently started a new medicine and the symptoms followed within a few weeks
Each area is treated differently
This is where patients are often disappointed by treatment, because a method that works very well for the underarms may not be the first choice for the palms.
Underarms: respond best to antiperspirants and botulinum toxin injections, and are the only area with a permanent sweat-gland-destroying procedure using microwave energy.
Palms: topical products are often not enough. Iontophoresis works well. Botulinum toxin injections also work but are more painful and may cause temporary hand weakness.
Soles: similar to the palms, but topical products are harder to absorb because the skin is thick, and foot odor and fungal infection often come along and need to be treated at the same time.
Face and scalp: can be injected but care is needed to avoid facial muscle weakness; oral medicines are often used alongside.
If your main problem is sweaty palms in particular, read the detailed article Sweaty Hands: Causes and Treatment, and if foot odor is also a problem, see Smelly Feet and Excessive Foot Sweating.
The treatment ladder: always start with the simplest step
The principle is to go from the lowest-risk, least expensive methods upward. No one should be sent for surgery at their first visit.
Step 1: High-strength antiperspirant
The main ingredient is aluminum chloride hexahydrate at about 10-20%, which works by temporarily blocking the sweat gland ducts. It is not an antibacterial or a deodorant. Almost every case where people say it did not work comes down to using it the wrong way:
Apply at bedtime, not in the morning, because sweat glands are least active at night, so the product can get into the ducts and block them.
The skin must be completely dry before applying. If it is still damp, acid forms and stings badly.
Wash it off in the morning and repeat every night at first. Once control is achieved, reduce to 2-3 times a week.
If it irritates, apply less often or ask your doctor about alternating with a moisturizer, rather than stopping altogether.
Step 2: Iontophoresis
The hands or feet are soaked in water through which a mild electric current passes, for about 20-30 minutes per session, several times a week at first, then tapering to a maintenance schedule to keep symptoms under control. It is safe, needs no medicine, and is especially suited to the palms and soles. The limitation is that it must be done regularly, and it is not suitable for people who are pregnant or who have implanted electronic devices.
Step 3: Botulinum toxin injections
It works by blocking the neurotransmitter that tells the sweat glands to work, so it cuts off the problem at the source of the signal. It works very well on the underarms, and generally controls symptoms for about 6-12 months before repeat injections are needed. It also works on the palms but is more painful and some people have temporary hand muscle weakness, so this should be discussed first, especially for people who use their hands for fine work.
Step 4: Oral medicines
Anticholinergic medicines such as glycopyrrolate and oxybutynin are used when sweating occurs in several areas at once or all over the body, where injecting specific areas does not meet the need. The trade-off is common side effects: dry mouth, blurred vision, constipation, and difficulty urinating. Caution is needed in people with angle-closure glaucoma or urination problems. They must be prescribed and monitored by a doctor.
Step 5: Permanent procedures
Microwave destruction of underarm sweat glands: gives a fairly permanent result because destroyed sweat glands do not regrow. It can be used only on the underarms.
Sympathetic nerve surgery (ETS): reserved as a last resort for severe palm sweating that has failed every other method, because of a major side effect, compensatory sweating in other areas, which is common and cannot be reversed. This must be clearly understood before deciding.
What you can do yourself during treatment
Choose cotton or breathable fabrics and avoid tight synthetic fabrics.
Use underarm sweat pads and change socks during the day. This does not reduce sweating, but it reduces follow-on problems such as odor and fungal infection.
Rotate your shoes rather than wearing the same pair every day, so they can dry completely.
Notice your own triggers, such as coffee, energy drinks, spicy food, and stress.
Manage stress and anxiety alongside treatment, because the two feed each other in a cycle.
Common misunderstandings
"Heavy sweating means the body is flushing out toxins." Not true. Sweat is almost entirely water and electrolytes, and its main job is to cool the body.
"Drink less water so you sweat less." Dangerous. It leads to dehydration without meaningfully reducing sweating.
"A regular roll-on is enough." Deodorants only deal with odor and do not reduce sweat. You need an antiperspirant that is strong enough.
"Botox injections will make the sweat come out somewhere else." Targeted injections do not cause the compensatory sweating seen after ETS surgery. The two work by different mechanisms.
"You just have to put up with it because it is hereditary." Genetics explains why it happens, but it does not mean it cannot be treated.
When to see a dermatologist
Ordinary antiperspirants have not brought it under control
Sweating interferes with work, study, or relationships
The skin where you sweat is becoming macerated, peeling, smelly, or has repeated fungal infections
You have signs of secondary excessive sweating as described above
You have started avoiding social situations or feel it is affecting your mental health. This one reason alone is good enough to seek treatment
Frequently asked questions about excessive sweating
Can excessive sweating be cured completely?
For the primary type, there is no method that cures it permanently in every area, but it can be controlled very well with the right treatment. Botulinum toxin injections control it for about 6-12 months at a time, while microwave treatment of the underarms gives a fairly permanent result. For the secondary type, treating the underlying disease usually brings sweating back to normal.
Is excessive sweating dangerous?
The condition itself is not life-threatening, but it greatly affects quality of life and makes the skin more prone to maceration, fungal infection, and sores. The concern is when it is a sign of another disease, especially when sweating is all over the body, occurs during sleep, or begins after age 25.
Do underarm Botox injections hurt, and how long do they last?
Small needles are used to inject shallowly at multiple points. It takes about 15-20 minutes, and numbing cream can be applied first. Most people tolerate it well. The effect lasts about 6-12 months before repeat injections. The palms hurt more because the skin is thick and has many nerve endings.
What should I do if antiperspirant stings?
Stinging is usually caused by applying it to skin that is still damp, or applying too often at the start. Dry the skin completely before applying, apply only at bedtime, wash it off in the morning, and temporarily reduce how often you use it. If it still stings a lot, consult a doctor to adjust the strength or change the product.
Is excessive sweating a sign of heart disease or cancer?
Sweating limited to the palms, soles, or underarms since the teenage years, which stops during sleep, has almost nothing to do with those diseases. But sweating all over the body, especially at night, together with weight loss, fever, or swollen lymph nodes, is a pattern that needs a serious search for the cause.
Is excessive sweating caused by stress alone?
Stress is a trigger that makes it worse, but it is not the whole cause. People with the primary type sweat heavily even on relaxed days. Effective treatment therefore has to address the sweat glands alongside stress management.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed August 16, 2026
If excessive sweating is getting in the way of daily life, the dermatology team at Siam Dermatology can assess the cause and plan treatment suited to the location and severity for each person. Consult us via LINE: @siamderm
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