Night Sweats: Causes and When to Worry

What counts as night sweats

Waking up warm because the bedroom is hot or you are under a heavy comforter is normal. True night sweats are drenching: your pajamas or sheets are damp enough that you need to change them, and it happens even when the room is cool. Doctors also pay attention to episodes that are less dramatic but happen night after night.

Your body temperature naturally dips during sleep. Anything that resets the brain's thermostat (the hypothalamus), adds heat, or triggers the stress hormone system can push the body to sweat to cool down. That is why night sweats have so many possible causes, from hormones to infection.

When to worry about night sweats

Most night sweats have a simple explanation. They are more likely to point to something that needs tests when they come with what doctors call "B symptoms" or other warning signs:

• Fever that comes and goes, especially in the evening
• Unexplained weight loss, generally more than 5% to 10% of body weight over 6 months
• Swollen lymph nodes that are painless, firm and growing
• A cough lasting more than 3 weeks, or coughing up blood
• Itching all over the body without a rash
• Persistent tiredness and body aches
• New sweats in someone with a weakened immune system, a heart valve problem or recent travel to areas where tuberculosis is common

Night sweats on their own, in an otherwise well person, are rarely due to cancer. In large studies of people visiting primary care with night sweats, most had no serious cause found. Still, sweats that persist for more than 2 to 3 weeks deserve a check, because a few simple tests can rule out the serious causes.

Common causes of night sweats

Menopause and perimenopause

Hot flashes that happen during sleep are the most common cause of night sweats in women in their 40s and 50s. Falling estrogen makes the hypothalamus over-sensitive to small rises in temperature. A flush of heat spreads over the chest, neck and face, followed by sweating and sometimes chills. They often start during perimenopause and can continue for several years after periods stop. Early menopause after surgery or cancer treatment can cause sudden, intense sweats.

Medicines

Many common medicines cause sweating as a side effect:

• antidepressants, especially SSRIs, SNRIs and tricyclics
• diabetes medicines that can cause low blood sugar overnight (insulin, sulfonylureas)
• hormone therapy that lowers estrogen or testosterone, such as tamoxifen, aromatase inhibitors and treatments for prostate cancer
• steroids such as prednisone
• acetaminophen and aspirin, when a fever breaks
• some blood pressure medicines, opioids and drugs for erectile dysfunction

If sweats started within weeks of a new medicine or dose change, the medicine is a likely cause. Do not stop a prescribed medicine without talking to your doctor.

Alcohol, caffeine and substance withdrawal

Alcohol widens blood vessels in the skin and disturbs sleep, so evening drinking commonly causes sweats. Withdrawal from alcohol, opioids or benzodiazepines causes heavy sweating along with shakiness and anxiety.

Anxiety and stress

Anxiety disorders, nightmares and panic attacks during sleep activate the fight-or-flight response, which raises heart rate and triggers sweating. These sweats often come with a racing heart and waking suddenly.

Sleep apnea

In sleep apnea, the airway collapses repeatedly during sleep. Each pause in breathing triggers a surge of adrenaline. Loud snoring, gasping, morning headaches and daytime sleepiness are clues. Treatment with CPAP often stops the sweats.

Acid reflux

Gastroesophageal reflux disease (GERD) is a recognized but often overlooked cause of night sweats, particularly in people with heartburn at night.

Idiopathic hyperhidrosis

Some people simply sweat more than others without any underlying illness. This is called primary hyperhidrosis. It usually starts in childhood or the teenage years and tends to affect the palms, soles and armpits during the day as well.

Serious causes of night sweats

These are less common but are the reason doctors take persistent night sweats seriously.

Infections

• Tuberculosis (TB): the classic cause of drenching night sweats, with weight loss, a long-lasting cough and fever. More likely after travel, migration from a high-TB country, homelessness, imprisonment or HIV infection.
• HIV: night sweats can occur in the first weeks after infection (with a flu-like illness and rash) and in advanced, untreated HIV.
• Endocarditis: infection of the heart valves causes fevers, sweats, tiredness and sometimes a new murmur. Risk is higher with artificial valves, heart defects and injection drug use.
• Bone infection and abscesses: osteomyelitis and deep abscesses can cause low-grade fever and sweats for weeks.
• Other infections: infectious mononucleosis, fungal infections such as histoplasmosis, and travel-related infections such as malaria.

Cancers

• Lymphoma: both Hodgkin and non-Hodgkin lymphoma can cause drenching sweats, fever, weight loss and painless swollen lymph nodes. Lymphoma is the cancer most strongly linked to night sweats.
• Leukemia: often with tiredness, easy bruising, frequent infections and paleness.
• Other cancers: less often, kidney, liver and other solid tumors.

Hormone problems

• Overactive thyroid: hyperthyroidism causes heat intolerance, sweating, weight loss, a fast heartbeat and tremor.
• Low blood sugar: in people with diabetes, overnight hypoglycemia causes sweating, nightmares and a headache on waking.
• Rare tumors: pheochromocytoma (attacks of sweating, pounding headache and very high blood pressure) and carcinoid syndrome (flushing and diarrhea).
• Low testosterone in men, including after prostate cancer treatment.

Inflammatory diseases

Conditions such as giant cell arteritis, rheumatoid arthritis and other autoimmune diseases can cause fever and sweats, usually with joint or muscle pain and stiffness.

Clues from accompanying symptoms

Night sweats after menopause

Sweats from menopause usually fade within a few years, although about 1 in 10 women still have hot flashes in their 60s and beyond. New, drenching sweats that start long after menopause has ended, or that return after years without symptoms, should be checked rather than assumed to be hormonal. This is especially true if you also feel achy or sore all over, are losing weight or have a fever.

In an older woman, sweats with widespread aching, stiffness in the shoulders and hips (worst in the morning) and tiredness can be caused by polymyalgia rheumatica, sometimes linked with giant cell arteritis. A new headache, scalp tenderness, jaw pain when chewing or any change in vision with these symptoms needs same-day medical attention, because giant cell arteritis can cause sudden loss of sight. Infection, thyroid disease, medicine side effects and, less often, lymphoma are other causes doctors will look for.

How doctors find the cause

Questions you will be asked

• How long have the sweats been happening, and how many nights a week?
• Do you need to change clothes or bedding?
• Have you had fever, weight loss, cough, itching or lumps?
• What medicines, supplements and alcohol do you take?
• Where have you traveled, and have you been around anyone with TB?
• For women, what is your menstrual and menopause history?
• Do you snore, or has a partner noticed you stop breathing?

Examination and tests

The doctor will check your temperature, weight, heart, lungs, lymph nodes, thyroid, liver and spleen. Common first tests are:

• complete blood count and blood film
• inflammatory markers (ESR and CRP)
• thyroid function tests
• blood sugar and HbA1c
• HIV test and, where relevant, a TB blood test or skin test
• chest X-ray

If these are normal and you have no other symptoms, the cause is usually benign. Further tests, such as blood cultures, an echocardiogram, CT scans or a lymph node biopsy, are used only when a specific cause is suspected. A sleep study is arranged if sleep apnea is likely.

How to stop night sweats

Treat the cause

• Menopause: hormone therapy is the most effective treatment for hot flashes and night sweats. Non-hormonal prescription options include some antidepressants, gabapentin and fezolinetant. Your doctor can weigh the benefits and risks for you.
• Medicine side effects: a dose change or switch often helps.
• Infections, thyroid disease and sleep apnea: sweats usually stop once these are treated.
• Low blood sugar at night: adjusting diabetes medicines or bedtime snacks with your diabetes team.

Things you can do tonight

• Keep the bedroom cool, around 60 to 67 °F (16 to 19 °C), and use a fan.
• Use layered, breathable cotton bedding and moisture-wicking sleepwear so you can remove layers.
• Keep a glass of cold water and a change of clothes by the bed.
• Avoid alcohol, caffeine, spicy food and heavy meals in the 2 to 3 hours before bed.
• Take a cool shower before sleep.
• For menopausal sweats, regular exercise, stopping smoking, losing excess weight and cognitive behavioral therapy (CBT) can reduce how bothersome they are.

Frequently asked questions

When should I worry about night sweats?

See a doctor if night sweats happen most nights for more than 2 to 3 weeks without an obvious cause, or if they come with fever, unexplained weight loss, swollen glands, a persistent cough or extreme tiredness. Get urgent help if sweats come with chest pain, confusion, breathing problems or signs of severe infection.

Can night sweats be a sign of cancer?

Yes, but rarely. Lymphoma and leukemia are the cancers most linked to night sweats. They usually come with other symptoms, such as painless swollen lymph nodes, weight loss, fever, itching or easy bruising. Night sweats alone in a person who otherwise feels well are much more likely to have a harmless cause.

Why am I suddenly sweating at night?

A sudden start often points to something new: a cold or flu, a new medicine or dose change, alcohol, stress, perimenopause or a warmer bedroom. If none of these fits, and the sweats continue for more than a couple of weeks, ask your doctor for blood tests to check for infection, thyroid problems and other causes.

What causes drenching night sweats after menopause has ended?

Late recurrence can come from medicines, an overactive thyroid, infection, low blood sugar, sleep apnea or inflammatory conditions such as polymyalgia rheumatica, especially when the whole body feels sore and stiff. Less often, it signals lymphoma. Because hormone changes should have settled, new drenching sweats years after menopause warrant a medical check.

Can anxiety cause night sweats?

Yes. Anxiety, stress, nightmares and nighttime panic attacks release adrenaline, which raises your heart rate and triggers sweating. These sweats often wake you suddenly with a pounding heart. Treating the anxiety, for example with CBT, usually reduces them. Persistent sweats with fever or weight loss should still be checked.

Are night sweats normal in men?

Night sweats can happen in men for the same reasons as in women: medicines, alcohol, infection, sleep apnea and anxiety. Low testosterone, including after treatment for prostate cancer, is a male-specific cause. Men with persistent sweats, fever or weight loss should see a doctor.