Night Sweats: What Causes Them and When to Worry

Causes by Clinical Context

References

Sources cited on this page. PubMed links open the original abstract.

1. Mold JW, Mathew MK, Belgore S, DeHaven M. Prevalence of night sweats in primary care patients: an OKPRN and TAFP-Net collaborative study. J Fam Pract. 2002;51(5):452–456. PMID 12019049

What causes night sweats – a clinical framework

Night sweats refers to drenching sweats that soak through clothing and bedding, not simply feeling warm at night. Doctors use a structured approach to narrow the cause, grouping possibilities into four broad categories:

• Hormonal: Menopause is the single most common cause in women aged 40–58. Falling oestrogen levels destabilise the hypothalamic thermostat. Male hypogonadism (low testosterone) causes similar sweats in men. Both are confirmed with a blood FSH/LH and sex hormone panel.
• Infectious: Tuberculosis (TB) classically causes night sweats, weight loss, and a chronic cough. HIV, endocarditis (heart valve infection), and brucellosis also feature prominent sweating. A full blood count (looking for lymphocytosis), ESR, CRP, HIV test, and chest X-ray are first-line investigations.
• Malignant: Lymphoma – both Hodgkin and non-Hodgkin – is the cancer most associated with drenching night sweats, often accompanied by unexplained weight loss and lymph node swelling (the "B symptoms"). Leukaemia and other haematological cancers can present similarly.
• Medication-related: Antidepressants (especially SSRIs and venlafaxine), tamoxifen, nifedipine, and opioids are among the most common drug causes. A medication review is essential before extensive investigation.

Blood tests that evaluate night sweats

The initial blood panel for persistent unexplained night sweats (lasting more than 4 weeks) typically includes:

• Full blood count (FBC): Anaemia, high white cells (infection/leukaemia), or thrombocytopenia can direct diagnosis.
• ESR and CRP: Elevated in infection, inflammation, and many cancers. A markedly elevated ESR (above 100 mm/hr) raises suspicion for lymphoma, myeloma, or TB.
• LFTs and LDH: Raised LDH (lactate dehydrogenase) is a non-specific marker of tissue turnover – significantly elevated in lymphoma.
• TSH: Hyperthyroidism causes heat intolerance and sweating at any time of day, but can feel worse at night.
• Fasting glucose / HbA1c: Hypoglycaemia (especially in people taking insulin or sulfonylureas) causes classic nocturnal sweats – the body's adrenaline response to low glucose.
• HIV test: HIV can present with constitutional symptoms including night sweats at seroconversion or in advanced disease.
• Sex hormone panel (FSH, LH, oestradiol or testosterone): Confirms menopause or hypogonadism.

If initial tests are unrevealing and sweats persist, a CT scan of the chest, abdomen, and pelvis is usually ordered to look for lymphadenopathy or occult tumour – particularly if weight loss or an elevated LDH accompanies the sweats.

When night sweats need urgent assessment

While most night sweats have a benign cause, certain "red flag" combinations warrant same-day or urgent review:

• Night sweats plus unexplained weight loss of more than 5% body weight in 3 months
• Night sweats plus persistent lymph node swelling (especially painless)
• Night sweats plus a chronic productive cough – TB until proven otherwise
• Night sweats in a person who is immunocompromised (HIV, on steroids, post-transplant)
• Fever accompanying the sweats

NICE guidance (NG12 – suspected cancer recognition) recommends urgent chest X-ray and blood tests within 2 weeks for patients presenting with night sweats alongside any of these features, and direct-access CT or haematology referral if lymphoma is suspected.