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Sleep hyperhidrosis, more commonly known as the night sweats, is the occurrence of excessive sweating (hyperhidrosis) during sleep. The sufferer may or may not also suffer from excessive perspiration while awake. Sleep hyperhidrosis may occur at any age, but is most commonly seen in early adulthood.
Night sweats may occur for genetic reasons and may be relatively harmless. However, they can be distressing and disrupt sleep patterns if severe; the patient may be frequently awakened due to the discomfort of damp sleepwear or bedding.
One of the most common causes of night sweats in women over 40 is the hormonal changes related to menopause and perimenopause. This is a very common occurrence during the menopause transition years and while annoying, it is not necessarily dangerous or a sign of underlying disease. Some women experience night sweats during pregnancy due to hormonal changes.
While night sweats might be relatively harmless, it can also be a sign of a serious underlying disease. It is important to distinguish night sweats due to medical causes from those that occur simply because the sleep environment is too warm, either because the bedroom is unusually hot or because there are too many covers on the bed. Night sweats caused by a medical condition or infection can be described as "severe hot flashes occurring at night that can drench sleepwear and sheets, which are not related to the environment." Some of the underlying medical conditions and infections that cause these severe night sweats can be life-threatening and should promptly be investigated by a medical practitioner.
Some people suffering from night sweats have found relief by wearing moisture-wicking pajamas and by having drinking water at hand.
Associated conditions 
- Acrodynia (childhood mercury poisoning)
- Anorexia Nervosa
- Brucellosis (a bacterial infection)
- Cerebral palsy
- Cerebral and brain stem strokes
- Chronic Fatigue Syndrome
- Epilepsy
- Familial dysautonomia
- Gastroesophageal Reflux Disease
- Head injury
- Hypoglycaemia (Chromium deficiency)
- Hypothalamic lesions
- Infectious Mononucleosis
- Influenza
- Lyme Disease
- Obstructive Sleep Apnea
- Posttraumatic stress disorder
- Pneumonia
- Pulmonary histoplasmosis
- Sarcoidosis
- Subacute endocarditis
- Urinary tract infection
Certain medications, anti-depressants (such as sertraline) have also been known to cause night sweats in some individuals. Another cause could be withdrawal from various drugs (opiates, benzodiazepines, alcohol, etc.).
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