People who suffer night sweats will typically wake in the night to find their bedclothes and bedding drenched, even if their bedroom temperature is cool. This abnormal sweating is annoying, but usually harmless.

However, night sweats can sometimes be a sign of an underlying medical condition, so you should see your GP if they keep happening and you're worried.

In the meantime, you can get a better idea of the possible cause of your night sweats by reading on. However, you should not use this page to diagnose yourself with a condition – always leave that to your doctor.

The medical term for night sweats is nocturnal hyperhidrosis, which literally means "night-time excessive sweating".

What is the likely cause?

The main conditions and medications that can cause night sweats are summarised below, although it should be noted that many of these conditions would cause other more specific symptoms as well:

• the menopause
• obstructive sleep apnoea – a condition that causes interrupted breathing during sleep 
• medication – antidepressants and some other psychiatric drugs can sometimes cause night sweats as a side effect, as can aspirin and the steroid drug prednisolone
• alcohol abuse or drug misuse – especially the use of heroin
• hypoglycaemia (low blood sugar), which is commonly associated with diabetes and taking insulin  
• infections – tuberculosis is the most common infection associated with night sweats, but sweating may also be caused by other infections, including endocarditis (inflammation of the heart valves), osteomyelitis (a bone infection), abscesses and HIV/AIDS
• cancer – night sweats can be an early symptom of certain cancers, such as lymphoma or leukaemia; however, this is unusual and cancer would cause other symptoms too, such as unintentional weight loss
• hormone disorders such as pheochromocytoma and carcinoid syndrome (tumours that cause the body to overproduce hormones) and an overactive thyroid gland
• gastro-oesophageal reflux disease (GORD) –  where stomach acid leaks out of the stomach and into the gullet, although night sweats are not a common symptom of this 

There may not be an identifiable cause for your night sweats, and it may just be an annoyance that happens every now and then. When the cause is unknown, it is referred to as idiopathic hyperhidrosis.