We all sweat when we get hot. It's one of our 'homeostatic mechanisms' - the ways our bodies are adapted to maintain the same constant internal environment. This is very important to allow all the processes going on inside our bodies to tick along smoothly.
Sweating helps your body lose heat by evaporation if your core temperature, deep inside your body, rises. In the same way, shivering or shutting down the circulation in your hands and feet helps warm your body up if you're cold.
But sometimes sweating, especially if the outside temperature isn't hot and you're not wearing too many layers or exercising hard, can be a sign that there's something going on.
What is a night sweat?
A night sweat is excess sweating at night. Although night sweats can occur if your bedroom is very hot or you have too many bedclothes on overnight, true night sweats occur at night. They can drench your nightclothes and are not related to being too warm in bed.
Night sweats are a symptom, not a medical condition in their own right. You can often get a clue to the underlying cause from other symptoms which go along with the sweats. For instance, if your night sweats have coincided with getting an infection like a nasty tummy bug or cough, the infection is usually the cause.
But you should see your doctor if you have persistent or very troublesome night sweats, partly to make sure there's nothing serious going on. But finding out the underlying cause might also mean your doctor can offer effective treatment.
What causes night sweats?
There are many different causes of night sweats. Some of the conditions that can cause night sweats include:
Night sweats are often a very common symptom many women experience during their menopause. This is related to not having enough oestrogen in the body.
If you're a woman in your late 40s or early 50s, your periods have stopped recently and you're also getting hot flushes (episodes of flushing usually affecting your face, arms and neck) during the day, it's highly likely that your night sweats are down to the menopause. Menopausal symptoms can also start below the age of 45 and before your periods have stopped completely.
If the night sweats are troublesome and you have other symptoms, there are several lifestyle changes which can help. If this isn't enough, taking hormone replacement therapy (HRT) can really help to improve your menopausal symptoms. See the separate leaflet called Menopause (including HRT).
Some tablets and medicines can cause night sweats as a side-effect. For example some antidepressants and aspirin can cause night sweats. See the separate leaflets called Antidepressants and Aspirin and Other Antiplatelet Medicines.
If your night sweats are due to to your medication it may be possible to take alternative medication. Your doctor will be able to discuss this with you.
Low blood sugar levels
Sometimes low blood glucose - called hypoglycaemia or 'hypos' - can cause sweating. If you are taking insulin or some types of oral diabetes medications such as sulfonylureas (for example, gliclazide or glipizide) then you may experience low sugar levels at night accompanied by sweating.
Hypos can also occur during the day, leading to:
- Feeling irritable or hungry.
- Poor concentration and irritability.
- Blurred vision.
- Confusion and problems with speaking.
- In severe cases, loss of consciousness.
It's extremely important to speak with your doctor if you think you might be suffering from hypos. They can lead to severe complications and even death, as well as affecting your ability to drive safely. Your doctor may be able to change your medication or your insulin dose to reduce your risks.
Most infections can cause a high temperature (fever) with some sweating; however, a fever at night causing night sweats is more common with certain types of infections. Tuberculosis (TB) is the infection most commonly associated with night sweats. See the separate leaflet called Tuberculosis.
However, infections caused by germs (bacterial infections), such as inflammation of the heart valves (infective endocarditis), inflammation within your bones (osteomyelitis), and abscesses, all may result in night sweats. See the separate leaflets called Infective Endocarditis, Osteomyelitis and Abscess.
Night sweats can also be a symptom of HIV infection. See the separate leaflet called HIV and AIDS.
Influenza usually causes a fever that comes and goes - it is not specifically associated with night sweats.
Night sweats can sometimes be an early symptom of some cancers. Although other causes of night sweats are much more likely as a reason for your night sweats, it is clearly very important to have cancer diagnosed and treated as soon as possible.
The most common type of cancer associated with night sweats is lymphoma. It is likely that you experience other symptoms such as fevers and weight loss if this is the underlying cause. See the separate leaflet called Hodgkin's Lymphoma.
Overactive thyroid gland (hyperthyroidism)
Sweating or flushing can be seen with hyperthyroidism. In this condition your thyroid gland is overactive. Other symptoms may include weight loss, feeling warm and losing weight without an obvious reason. See the separate leaflet called Thyroid Gland (Hyperthyroidism).
There are many other conditions that may cause night sweats. For example, drinking too much alcohol or taking illegal drugs can cause night sweats. See the separate leaflets called Alcoholism and Problem Drinking and Recreational Drugs.
A condition called hyperhidrosis causes too much sweating. People with this condition sweat too much in the day and also during the night. See the separate leaflet called Excessive Sweating (Hyperhidrosis).
When should you see a doctor about your night sweats?
You should see your doctor if you have regular night sweats. In addition, if you also have a high temperature (fever) or other symptoms, such as unexplained weight loss, you should also go to your doctor. Your doctor may arrange for you to have some tests such as blood tests or X-rays to determine the cause of your night sweats. The treatment of your night sweats will depend on the underlying cause.