It's something we've probably all experienced - jolting awake in the early hours of the morning to find the sheets drenched in sweat. Clearly, night sweats are no fun. What can be less obvious is why you're experiencing them and what it might mean from a medical perspective.
"Sweating at night is a normal phenomenon and experienced by most people at some point. The term 'night sweats' refers to excessive sweating during the night, where severe hot flushes can consistently leave you waking up with soaking wet clothes and sheets," says Dr Farah Gilani, a GP at Medicspot.
In other words, if your bedroom is too warm or your duvet too thick, it'd be inaccurate to think of this as 'night sweats' - you've simply overheated. In one study of 2,267 patients visiting a GP, 41% said they'd experienced excessive sweating at night over the previous month.
True night sweats are unrelated to the environment and occur independently of outside temperature. It's also important to distinguish night sweats from flushing, warmth or redness of the face and body.
Some common causes
In rare cases, night sweats can be a sign of an underlying medical condition, including (occasionally) cancer. But before you panic and assume the worst-case scenario, it's worth remembering that night sweats can have a wide range of different causes.
"Night sweats can be caused by a number of medical conditions. Some of the most common causes include the menopause, anxiety, medicines, low blood sugar, infections, alcohol or drug misuse, and hyperhidrosis," says Gilani.
If you're a woman over 40, night sweats are often caused by the hormonal changes sparked by menopause and perimenopause. Up to 85% of women experience hot flushes during menopause, and in 55% of women the hot flushes begin before any menstrual irregularities.
Anxiety can lead to night sweats because the body's stress response has been activated (with the concomitant changes in metabolism, heart rate, body temperature etc). Particularly if you've been experiencing nightmares, it's normal to have a physiological response to that fear.
On a similar note, low blood sugar can cause the body to produce excessive adrenaline, which in turn can lead to night sweats. This is a common problem in those with diabetes, and can also happen if you've drunk too much alcohol before bed.
Certain medications can be the culprit, particularly antidepressants. Although it can be hard to estimate the true prevalence, it is thought that up to 22% of people taking SSRIs experience excessive sweating. Likewise, a number of pain medications, diabetes medications and hormonal medications list sweating as a potential side effect.
In terms of infections, the main ones associated with night sweats are tuberculosis and HIV. While these may sound pretty scary, they're far from the most likely diagnosis and would almost invariably be accompanied by other symptoms too.
Finally, hyperhidrosis is just another word for excessive sweating (both during the night and day). This can be a condition in its own right, and doesn't have to be a symptom of something else. You may want to visit the GP if it's interfering with your life.
When to see the GP
As Gilani explains, if you're worried about night sweats, speaking with a GP can help. Because there are so many potential causes - and no easy way of differentiating one type of sweating from another - they will ask you a number of questions to build up a fuller picture.
"To investigate night sweats, a GP will take your medical history, and may examine you to determine if there is an underlying medical condition. Depending on the findings, they may then order tests such as blood tests, X-rays, or other specialised investigations," she says.
You should always see the GP if your night sweats are accompanied by a very high temperature, cough, diarrhoea, localised pain or other symptoms of concern. And while night sweats every so often are probably nothing to worry about, it's worth seeking advice if they're persistent.
"If you find that you are also losing weight for no apparent reason, it's important to see a GP as this could be a sign of a more serious condition," says Gilani. "Also, if you have been diagnosed with lymphoma or HIV, night sweats accompanied by unexplained weight loss may be a warning sign that your disease is progressing."
If your night sweats can be traced to menopause, you may want to look into hormone replacement therapy (HRT). And if the GP believes your medication is to blame, solving the problem may be as simple as prescribing something different.
Most of the time, though, lifestyle changes are sufficient to treat night sweats and medication isn't necessary. For instance, you might try avoiding hot spicy food, alcohol and caffeine; practising relaxation breathing exercises before bed; and improving your 'sleep hygiene'.
"By making simple adjustments to your sleeping habits, including removing blankets from your bed, having your bedroom window open at night or wearing lighter pyjamas, you can help prevent and alleviate night sweats," says Gilani.