What Causes Night Sweats?

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, or 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, typically 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 apnoea 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 typically check#

A careful history first, because the pattern usually gives the answer. Then, if the sweats are genuinely 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.