What Causes Night Sweats?
A doctor explains what causes night sweats, how to tell a warm bedroom from a medical cause, and which drenching sweats need investigation soon.
See a doctor promptly if
- Sweats that soak nightclothes or sheets most nights for more than two weeks
- Night sweats with unintentional weight loss or persistent fever
- Night sweats with a cough lasting over two weeks, or with new lumps in the neck, armpit or groin
The short version
- Most night sweats come from your surroundings or your hormones. Think a warm room, heavy bedding, alcohol, anxiety, or the hormone shifts of perimenopause.
- Sweats that drench nightclothes or bedding, night after night, are a different symptom. Those need medical assessment.
- Night sweats with unexplained weight loss, a persistent fever, or a lasting cough need prompt investigation.
Most night sweats are not a disease. A warm bedroom, a synthetic duvet, alcohol in the evening, a heavy late meal, or the hormonal fluctuations of perimenopause explain the large majority, and all of them are easier to change than people expect.
The important distinction is severity, not frequency. Waking a little damp is normal. Drenching sweats that force you to change your nightclothes or sheets, happening most nights for more than a couple of weeks, are a different symptom and should be assessed.
Why the body sweats at night#
Core temperature naturally falls in the first half of the night, and the body sheds heat by widening skin vessels and sweating.
Anything that raises heat production or blocks heat loss exaggerates that normal process:
- Too many layers
- A room above roughly 19 to 21 degrees Celsius
- A mattress that traps heat
- Alcohol widening blood vessels
- Spicy food and exercise close to bedtime
The common causes, in rough order#
Environment and habits. Bedding, room temperature, alcohol, late heavy meals, and late exercise. Worth fixing first because it is free and often decisive.
Hormonal change. Perimenopause is one of the most common causes in women from the late thirties onwards, usually with hot flushes in the day and irregular periods. Thyroid overactivity also produces sweating, along with weight loss, tremor and palpitations.
Infection. Any infection with a fever causes sweats as the temperature breaks. The ones that matter are those that persist: tuberculosis is a leading global cause of true night sweats and classically comes with weeks of cough, fever and weight loss. HIV and some abscesses do the same.
Medicines. Certain antidepressants, hormone therapies, and medicines that lower blood sugar overnight. Low blood sugar at night is a particular cause in people treated for diabetes, often with a headache or confusion on waking.
Anxiety and sleep disorders. Adrenaline surges, nightmares, and obstructive sleep apnea all produce genuine sweating.
Cancers. Lymphoma and some leukaemias cause drenching night sweats, but almost never in isolation. They come with weight loss, fever, itching, or new painless lumps. This is the least common cause on the list and the one people fear most.
What a doctor will usually check#
A careful history first, because the pattern usually gives the answer. Then, if the sweats are really drenching, a small standard set: full blood count, inflammatory markers, thyroid function, glucose or HbA1c, and depending on the region and story, tuberculosis and HIV testing and a chest X-ray.
When to get seen soon#
Book an appointment if sweats soak your bedding most nights for over two weeks, or if they come with weight loss you did not intend, persistent fever, a cough lasting more than two weeks, or new painless lumps in the neck, armpit or groin. These combinations move the problem up the priority list considerably.
The wider picture#
Night sweats often arrive alongside exhaustion, and the fuller guide to persistent tiredness sets out the same core blood tests that usually explain both together.
Should this go to a doctor?
Three honest answers, a plain answer back.
Before the day you need it
Every home needs one box: bandages, sterile gauze, tape, antiseptic, tweezers, gloves. Buy it before the day you need it, because that day does not announce itself.
Buying through this link supports the free library with a small commission. It never changes a pick.
A question about your own situation?
One question, answered personally by a doctor in writing within 24 hours.
Common questions
How do I tell ordinary sweating from a medical night sweat?
Can anxiety cause night sweats?
Which medicines often cause them?
People also ask
Not what you were looking for?
Say what you came for and we will take you there.
