Why Am I Sweating So Much?
If you regularly soak through shirts in a cool office, avoid handshakes because your palms are dripping, or wake up to damp bedding, you have probably asked yourself two questions: why is this happening, and is it a sign of something serious?
The honest answer for most people is reassuring. Excessive sweating usually means primary hyperhidrosis — a common, harmless (though miserable) condition where the sweat glands are simply overactive. It affects an estimated 1–3% of the population, and the NHS treats it as a recognised medical condition, not a hygiene problem.
Sometimes, though, sweating is a symptom of something else — a secondary cause such as a thyroid problem, diabetes, menopause, a medication, or an infection. The pattern of your sweating is the biggest clue to which camp you fall into, and that is what this guide covers: the causes, the symptom patterns that distinguish them, the red flags, and what actually happens when you see a GP about it.
Primary vs Secondary Hyperhidrosis: The Crucial Distinction
Doctors split excessive sweating into two categories, and everything about diagnosis and treatment flows from which one you have. Our guide to the types of hyperhidrosis covers this in depth, but here is the short version:
- Primary (focal) hyperhidrosis — overactive sweating in specific areas with no underlying disease. It is thought to be caused by overactivity in the sympathetic nerve supply to the sweat glands, and it clearly runs in families: around one to two thirds of people with primary hyperhidrosis have a relative with it too.
- Secondary hyperhidrosis — sweating caused by something else: a medical condition, a hormonal change, or a medication. Treat or address the underlying cause and the sweating usually improves.
| Feature | Primary hyperhidrosis | Secondary hyperhidrosis | |---|---|---| | Where you sweat | Focal — palms, soles, underarms, face/scalp | Generalised — all over the body | | Symmetry | Both sides equally | May be generalised or, rarely, one-sided | | When it started | Childhood or adolescence, almost always before 25 | Any age; new onset in adulthood is typical | | Sweating during sleep | Stops — night sweats are not typical | Often continues; true night sweats are common | | Family history | Frequently yes | Usually no | | Episodes | At least weekly, often triggered by stress or nothing at all | Tracks the underlying cause |
If your sweating is focal, symmetric, started young, stops at night and someone else in your family has it, that pattern points strongly to primary hyperhidrosis. If it is new, generalised or waking you at night, keep reading — the secondary causes below deserve a look.
What Causes Primary Hyperhidrosis?
Nobody fully knows — which is frustrating but worth saying plainly. The current understanding is that the sympathetic nervous system (the "fight or flight" wiring that controls sweat glands) is set too sensitively. The sweat glands themselves are normal in number and size; they are simply receiving too many "sweat now" signals, especially in response to emotion and stress.
The genetic link is well established. Primary hyperhidrosis clusters in families, and if it started for you in childhood or your early teens, there is a fair chance a parent, sibling or grandparent quietly dealt with the same thing.
What primary hyperhidrosis is not caused by: poor hygiene, being unfit, diet alone, or anxiety alone — although stress and anxiety amplify it significantly, and the embarrassment it causes can create a vicious sweat–worry–sweat loop.
Secondary Causes of Excessive Sweating
This is the "what is excessive sweating a sign of?" list. None of these mean your sweating is caused by them — but they are what a GP will consider, roughly in order of how commonly they turn up.
Thyroid Problems
An overactive thyroid (hyperthyroidism) speeds up your metabolism, and heat intolerance with sweating is a classic symptom. Clues that point this way: sweating alongside unintentional weight loss despite a good appetite, a racing or irregular heartbeat, tremor, irritability and feeling constantly warm. A simple blood test settles it either way.
Diabetes and Low Blood Sugar
Sweating relates to diabetes in two ways. Hypoglycaemia (low blood sugar) triggers a surge of adrenaline that causes sudden, cold, clammy sweating — familiar to anyone on insulin or sulfonylureas. Separately, long-standing diabetes can damage the nerves controlling sweat glands, causing unusual patterns such as gustatory sweating (facial sweating when eating).
Menopause and Hormonal Changes
Falling oestrogen levels narrow the brain's "thermoneutral zone", so tiny rises in core temperature trigger a full flush-and-sweat response. Hot flushes and night sweats affect up to 80% of women through perimenopause and menopause. Pregnancy and, in men, low testosterone can drive similar sweating. If this sounds like you, our dedicated guide to hyperhidrosis and menopause covers it properly.
Medications
A surprisingly long list of common medicines causes sweating as a side effect:
- Antidepressants — the biggest group. SSRIs and SNRIs cause excessive sweating in roughly 5–20% of people taking them; sertraline and sweating is one of the most common combinations we get asked about.
- Opioid painkillers — morphine, codeine, tramadol.
- Hormonal treatments — tamoxifen, GnRH analogues used for prostate cancer and endometriosis.
- Diabetes medications — via episodes of low blood sugar.
- Withdrawal — stopping alcohol, opioids or benzodiazepines can cause marked sweating.
If your sweating started within weeks of a new prescription, mention it to your GP — but do not stop a prescribed medication on your own.
Anxiety and Emotional Sweating
Anxiety genuinely causes sweating — the sympathetic nervous system does not distinguish between a tiger and a presentation. For some people, sweating is essentially confined to stressful situations; for others, anxiety pours fuel on pre-existing primary hyperhidrosis. Because the loop runs both ways, addressing the anxiety and the sweating together works better than either alone.
Infections
Persistent or recurring infections — most classically tuberculosis, but also endocarditis, HIV and bone infections — can cause drenching night sweats, often with fever and feeling generally unwell. This is uncommon, but it is why "sweating plus fever" changes the conversation at the GP.
Rarer Causes Worth Knowing About
These are rare, and we include them for completeness rather than alarm:
- Lymphoma and other cancers — night sweats with weight loss, fatigue or swollen lymph nodes.
- Phaeochromocytoma — a rare adrenal tumour causing episodes of sweating, pounding heartbeat and high blood pressure.
- Carcinoid syndrome — flushing and sweating with diarrhoea.
- Neurological conditions — Parkinson's disease, spinal cord injury, or nerve damage causing asymmetric sweating.
Hyperhidrosis Symptoms: The Patterns That Matter
Symptoms of hyperhidrosis are not just "sweating a lot" — the pattern is diagnostic. Doctors (including NICE's criteria for primary focal hyperhidrosis) look for:
- Focal sweating in one or more of: palms, soles, underarms, face/scalp
- Both sides affected symmetrically
- At least one episode a week
- Onset before age 25
- A positive family history
- Sweating that stops during sleep
- Real impact on daily life — ruined paperwork, avoided handshakes, multiple shirt changes, social withdrawal
Tick most of those boxes and primary hyperhidrosis is far and away the most likely explanation. The mirror-image pattern — generalised sweating, new onset in adulthood, present at night, no family history — is what suggests a secondary cause. If night sweats are your main issue, our guide to sweating at night walks through the causes specific to nocturnal sweating.
Red flags — see your GP promptly if excessive sweating comes with any of the following:
- Drenching night sweats that soak bedding
- Unexplained weight loss
- Fever or feeling persistently unwell
- Swollen lymph nodes
- Sweating on one side of the body only
- Chest pain, palpitations or breathlessness with sweating (call 999 if sudden and severe)
The combination of night sweats + weight loss + fever in particular warrants prompt assessment. Most people investigated for these turn out to have something treatable and benign — but this trio should never be sat on.
For a fuller breakdown of when sweating justifies an appointment and which specialist you might be referred to, see when to see a doctor about sweating.
What Happens at the GP
Knowing what to expect makes the appointment easier to book. A typical work-up looks like this:
- History. When did it start? Where do you sweat? Does it happen at night? Any weight loss, fever or new medications? Family history? This conversation alone usually separates primary from secondary.
- Examination. A general check, sometimes including your thyroid, heart rate and lymph nodes.
- Tests — only if needed. If your pattern is classic primary hyperhidrosis, no blood tests may be necessary. If a secondary cause is plausible, expect thyroid function tests, HbA1c or glucose, a full blood count and inflammatory markers; occasionally a chest X-ray or more specific tests follow.
- Treatment or referral. Confirmed primary hyperhidrosis opens the door to a genuine ladder of treatments — from prescription-strength antiperspirants and iontophoresis to oral medication, Botox and beyond. Our complete guide to hyperhidrosis treatment covers every rung in order.
One practical tip: keep a simple one-week sweat diary before your appointment (when, where on your body, what you were doing, night or day). It compresses months of frustration into evidence a GP can act on in a ten-minute slot.
The Bottom Line
Excessive sweating is nearly always one of two stories. The common one: primary hyperhidrosis — genetic, focal, starts young, stops at night, and very treatable. The less common one: a secondary cause such as thyroid disease, diabetes, menopause, anxiety or a medication — usually identifiable from the pattern and a couple of blood tests, and usually fixable at the source.
Either way, the worst option is the one most sufferers choose for years: quietly putting up with it. This site is educational and affiliate-supported, not a substitute for medical advice — if your sweating is affecting your life, or any red flag above applies, your GP is the right first step.