Excessive sweating happens when your body’s cooling system overreacts, producing far more sweat than you need to regulate temperature. The cause is either a malfunction in the nerves that control your sweat glands (primary hyperhidrosis) or an underlying medical condition, medication, or hormonal change that triggers sweating as a side effect (secondary hyperhidrosis). About 3% of the population deals with sweating significant enough to interfere with daily life.
How Your Body Produces Sweat
Your sweat glands are controlled by the sympathetic nervous system, which is the same network responsible for your fight-or-flight response. When something raises your core temperature or triggers a stress response, a region of the brain called the hypothalamus sends signals down through the spinal cord and out to your sweat glands. At the end of that nerve chain, a chemical messenger called acetylcholine binds to receptors on the glands and tells them to start producing sweat.
This system responds to two types of triggers. Heat and physical activity activate the thermoregulatory pathway, which is your body’s way of cooling itself. Stress, anxiety, and emotional reactions activate a separate pathway governed by a different brain region. Both use the same chemical messenger and the same sweat glands, which is why you can be drenched after a run or during a job interview.
In people with excessive sweating, the problem isn’t the sweat glands themselves. The glands are normal in size and number. The prevailing theory is that the sympathetic nerves feeding those glands are hyperexcitable, firing more intensely or more frequently than they should. That floods the glands with acetylcholine, and the result is a sweat response far out of proportion to whatever triggered it.
Primary Hyperhidrosis: No Underlying Cause
Primary hyperhidrosis is the most common form. It starts without any identifiable medical reason and typically appears before age 25, often during childhood or adolescence. It affects specific, symmetrical areas of the body: both palms, both underarms, both soles of the feet, or the face and scalp. The sweating is bilateral, meaning if your left palm sweats excessively, your right palm does too.
Clinically, primary hyperhidrosis is defined as focal, visible, excessive sweating lasting longer than six months with no apparent cause, plus at least two of the following: bilateral and symmetric pattern, impairment of daily activities, episodes at least once per week, onset before age 25, no sweating during sleep, and a positive family history. That last point matters. If one of your parents deals with excessively sweaty palms, your chances of having the same problem go up significantly.
One of the most telling features is that primary hyperhidrosis stops during sleep. Your sweat glands don’t activate at night, which distinguishes it clearly from conditions where sweating continues around the clock or worsens at night.
Medical Conditions That Cause Sweating
When excessive sweating is caused by something else in the body, it’s classified as secondary hyperhidrosis. Unlike primary hyperhidrosis, secondary sweating can be generalized (all over the body), can start at any age, and often occurs during sleep. Several categories of medical conditions are responsible.
Thyroid Problems
An overactive thyroid produces too much of a hormone called thyroxine, which speeds up your metabolism. When your metabolic rate climbs, your body generates more internal heat, and sweating is one of the first signs. If you’re sweating more than usual and also losing weight, feeling jittery, or noticing a rapid heartbeat, your thyroid is worth investigating.
Blood Sugar Drops
If you have diabetes, sudden drenching sweat can signal low blood sugar. Hypoglycemia triggers your body’s fight-or-flight response, and one of the fastest visible results is profuse sweating, often accompanied by shakiness, confusion, and a racing heart. This type of sweating comes on quickly and resolves once blood sugar is corrected.
Infections and Cancer
Night sweats that drench your sheets deserve attention, especially combined with unexplained weight loss, fever, or fatigue. Tuberculosis is a classic cause of drenching night sweats, as are certain cancers, particularly lymphoma. In lymphoma, the combination of fever, drenching night sweats, and weight loss is considered a prognostic indicator. Swollen lymph nodes that persist for more than four to six weeks alongside night sweats are a red flag that warrants prompt evaluation. A travel history can also help determine the likelihood of infections like tuberculosis.
Hormonal Transitions
Menopause is one of the most common causes of excessive sweating in women over 40. As estrogen levels decline, the brain’s thermoregulatory zone narrows dramatically. Normally, your body tolerates small fluctuations in core temperature without reacting. During menopause, that tolerance window shrinks, so even a tiny rise in core temperature can trigger a full-blown heat dissipation response: flushing, intense feelings of internal heat, and profuse sweating. These episodes are called hot flashes during the day and night sweats when they happen during sleep.
The relationship between estrogen and hot flashes is complicated. Estrogen therapy virtually eliminates them, which confirms that estrogen plays a role. But researchers have found no consistent difference in estrogen levels between women who get hot flashes and those who don’t. Elevated sympathetic nerve activity also contributes to narrowing the thermoregulatory zone, which is why stress and anxiety can make hot flashes worse.
Pregnancy causes a similar pattern. Hormonal shifts combined with an increased metabolic rate raise core body temperature, leading to sweating that many women find surprising in the second and third trimesters.
Medications That Trigger Sweating
Drug-induced sweating is more common than most people realize, and it’s one of the first things to consider if your excessive sweating started around the same time as a new prescription. The medication classes most frequently linked to hyperhidrosis include:
- Antidepressants: SSRIs (like fluoxetine and paroxetine), SNRIs (like venlafaxine), and older tricyclic antidepressants are among the most common culprits. Sweating is a well-documented side effect across all three classes.
- Opioid pain medications: Codeine, morphine, oxycodone, tramadol, and fentanyl all cause sweating through their effects on the nervous system.
- Thyroid medications: Levothyroxine, if dosed too high, mimics an overactive thyroid and can cause sweating as part of that picture.
- Steroids: Corticosteroids like prednisone, dexamethasone, and hydrocortisone affect hormonal function and can trigger sweating.
- Cholinesterase inhibitors: Used primarily for dementia, these medications increase acetylcholine levels, the same chemical messenger that activates sweat glands.
If you suspect a medication is causing your sweating, the timing is usually the strongest clue. Sweating that began within weeks of starting or increasing a dose points strongly toward the drug.
Anxiety and Emotional Sweating
Anxiety and excessive sweating have a frustrating, circular relationship. Stress and emotional arousal activate the sympathetic nervous system, which triggers sweating in areas like the palms, soles, underarms, and face. These are the same areas affected by primary hyperhidrosis, and in many people the two overlap: they have overactive sweat glands that respond even more aggressively to emotional triggers.
Emotional sweating is governed by a different brain region than heat-related sweating. The anterior cingulate cortex, which processes emotions and social awareness, drives sweat responses to embarrassment, anxiety, and fear, while the hypothalamus handles temperature regulation. This is why you can break into a cold sweat during a presentation in a perfectly cool room. For people with primary hyperhidrosis, the added layer of anxiety about sweating itself can amplify the problem, creating a feedback loop that’s difficult to break without addressing both the physical and psychological components.
How to Tell Which Type You Have
The pattern of your sweating is the single most useful diagnostic clue. Sweating limited to your palms, soles, underarms, or face, present since your teens, worse during the day, and absent during sleep points to primary hyperhidrosis. Sweating that is generalized, started later in life, happens at night, or appeared alongside other symptoms suggests a secondary cause that needs investigation.
In clinical settings, sweating can be measured precisely. A gravimetric test collects sweat on filter paper for a set period. Diagnostic thresholds are lower than you might expect: for underarm sweating, anything above 20 milligrams per minute for men or 10 milligrams per minute for women qualifies. For palms, the threshold is 30 to 40 milligrams per minute. In practice, though, most diagnoses are made based on history and symptom pattern rather than sweat measurement.
Secondary hyperhidrosis typically prompts blood work to check thyroid function, blood sugar levels, and markers for infection or inflammation. Night sweats combined with weight loss, persistent fever, fatigue, or easy bruising warrant a more urgent workup to rule out malignancy or serious infection.