Why do I sweat so much in my sleep and what can I do about it?

You fall asleep at a comfortable temperature — not too hot, not too cold — only to wake up a few hours later drenched in sweat. Sometimes, your pyjamas are soaked through, and you might even feel the need to change your sheets before returning to sleep. You’re wet, uncomfortable and maybe a little worried.

What is going on?

Night sweats are “a weird symptom, because mostly they’re harmless, but every once in a while, they’re not, so it’s certainly something that we always take seriously,” said Dr Kate Rowland, an associate professor of family medicine at Rush University in Aurora, Illinois.

There are many potential causes of night sweats, so when patients tell Dr Rowland that they’re waking up soaked, she’ll want to know more. “One of the first things we ask is ‘how warm is it in your room’?” she said.

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The National Sleep Foundation in America recommends a bedroom temperature between 60 and 67 degrees (15.6 to 19.4 degrees Celsius) for comfortable sleep. It’s not usually a problem keeping the night time temperature low in Ireland, but if you’re not able to keep your bedroom that cool, you can try adding a strategically placed fan, Dr Rowland said. Switching to lighter bedding or sleepwear might also help.

Our usual circadian rhythm includes a small, steady decline in core body temperature throughout the night, and sweating is a ‘normal, physiologic response’

If you’re sweating at night even after taking these steps to cool your sleep set-up, see a doctor to consider possible medical causes. He or she will likely ask how long and how frequently you’ve been having night sweats, whether they’re mild or they drench your pyjamas, and if you have additional symptoms such as fever, weight loss, fatigue, cough, shortness of breath or pain.

Any infection that causes a fever might result in sweating during the day or night, but a few serious illnesses — including tuberculosis, HIV infection, endocarditis (inflammation of the lining of your heart valves and chambers), malaria and mononucleosis — have been specifically associated with night sweats. And rarely, severe night sweats may be a symptom of a cancer such as lymphoma, Dr Rowland said.

“You can narrow things down pretty quickly with a few lab tests and a few detective-like questions,” said Dr Andrea Matsumura, a sleep medicine physician at the Oregon Clinic in Portland.

Dr Matsumura said she often sees patients in the menopausal transition whose sleep is fragmented by night sweats; along with hot flashes, these often begin several years before the final menstrual cycle and can persist for years afterward. If menopausal night sweats are interfering with a good night’s sleep, talk to your healthcare provider about treatment options, she said.

Among her patients, excessive night time sweating occurs “typically because they’re having some sort of abnormal breathing in their sleep, and that’s a sign of sleep apnoea,” Dr Matsumura said. Studies have found that night sweats can also be associated with insomnia, restless legs syndrome and narcolepsy.

Finally, many medications can cause night sweats. Among the most common culprits are antidepressants, diabetes medications and certain hormonal therapies. If a medication seems to be a cause, Dr Rowland will talk to her patients about the risks and benefits of stopping or changing the medication, depending on how bothersome the night sweats are.

Otherwise, sweating in sleep may just be a part of how your body regulates its temperature at night, Dr Rowland said. Our usual circadian rhythm includes a small, steady decline in core body temperature throughout the night, and sweating is a “normal, physiologic response” that may help you reach or maintain that lower temperature, she added. And “some people sweat more than other people do.”

Normal or not, night sweats can be uncomfortable and disruptive to sleep. In addition to regulating the temperature of your sleep set-up, Dr Matsumura recommended avoiding exercise, drinking alcohol or hot beverages, and eating a heavy meal too close to bedtime, all of which she said can cause sweating during the night.

If you normally sleep with a partner, you might also try sleeping separately for a few nights to see if that helps, Dr Rowland said.

Very often, coping with night sweats means performing a series of individual experiments in pursuit of a more comfortable snooze. “There’s nothing magic,” Dr Rowland said. “Different things work for different people.” — This article originally appeared in the New York Times