Night Sweats (Nighttime Perspiration, Sleep Sweating)

Sweating or perspiring is a skin response aimed at cooling down the body.  It is one of several mechanisms to regulate the body temperature. Heat is generated internally by the body’s metabolic activity and dissipated from the skin surface. The evaporation of sweat from the skin surface assists with the cooling effect. Normally heat dissipation will occur without the need for significant sweating if the environment is cold and activity is minimal. However, large amounts of sweat is necessary mainly in hot environments or when the metabolic activity is raised, like during exercise. Sweat regulation is controlled by the autonomic nervous system and apart from a hot environment and exercise, it may also be triggered with certain emotions and illnesses. Some people sweat more than others despite the environmental conditions and this may be due to increased sympathetic activity. At times this sweating can be excessive. Another phenomenon known as night sweats is nighttime perspiration that could be related to underlying disease.

What are night sweats?

Night sweats is the term for excessive nighttime perspiration often while asleep. It is also known as sleep hyperhidrosis. Despite the term ‘night sweats’, it can also occur during the day when asleep. It is important to note that any cause of excessive sweating may be worse at night and should be differentiated from night sweats specifically. With night sweats, a person may experience sweating during the day but it is not as profuse as the nighttime episodes. Night sweats need to be carefully assessed as it may be a sign of serious underlying diseases, particularly infections. Often night sweats are reported yet may just be perspiration due to overheating like using too much of clothing or being covered with too many blankets especially in a hot environment.

Although night sweats may present with just mild perspiration, it is typically seen as profuse or excessive perspiration. Night clothes and even bedding is soaked. Patients may wake up when the dripping sweat disturbs the sleep or moisture of clothing and linen becomes uncomfortable. Night sweats that occur as a once off episode and does not warrant significant cause for concern in these cases. However, daily episodes or recurrent bouts, even with a short period of no night sweating, needs to be assessed by a medical professional. Severe night sweats may not only warrant a change in clothing but a person may even need to bathe to relieve the discomfort.

Causes of Night Sweating

Two points need to be considered before conclusively identifying nighttime perspiration as night sweats specifically :

  • Is the person dressed too warmly during sleep, using heavy or excessive covering or sleeping in a hot room with inadequate cooling facilities?
  • If YES then sleep with lighter clothing and thinner bedding and try to utilize available cooling methods.
  • Are there other signs or symptoms of disease, particularly changes in body temperature, malaise, pain, weight loss and/or changes in appetite?
  • If YES then the night sweats may be a clinical feature of underlying disease.

Night sweats may be seen with any fever. Therefore the cause of acute fever, chronic fever and fever of unknown origin need to be taken into consideration.


Any infection can present with night sweats but it is more common with deeper infections than those affecting the superficial areas. Infectious diseases that are more likely to present with night sweats includes :

  • Abscess – localized accumulated of pus due to a walled-off site of infection.
  • Endocarditis – infection of the heart lining and valves.
  • Hepatitis – infection of the liver.
  • HIV (human immunodeficiency virus) and AIDS (acquired immune deficiency syndrome).
  • Influenza (flu) and the common cold.
  • Osteomyelitis – infection of the bone.
  • Tuberculosis – infection with the Mycobacterium tuberculosis bacteria that primarily affects the lungs.


Night sweats are an early symptom of cancer (malignant tumors) and can often be the only symptom at the outset. Although it can arise with cancer at any site in the body, it is more frequently seen with :

  • Leukemia – cancer of the blood or bone marrow.
  • Lymphoma – cancer of the lymph node (Hodgkin’s and non-Hodgkin’s).
  • Carcinoid syndrome – due to chemicals secreted from carcinoid tumors.

Night sweats may also be seen with benign tumors also this is uncommon. It may be seen with :

  • Pheochromocytoma – rare adrenal gland tumor.


Damage or disease of the brain or nerves may lead to night sweats. This is mainly as a result of disruptions in temperature regulation and controlling the activity of sweat glands.

  • Autonomic neuropathy – disorder of the nerves that control the involuntary functions of the body.
  • Hypothalamic lesions – damage or disease of the hypothalamus.
  • Stroke – disruption in brain activity as a result of death of a portion of brain tissue.
  • Spinal stroke – death or spinal cord tissue due to interrupted blood supply.
  • Syringomelia – fluid-filled cyst within the spinal cord.


The abnormal action of certain hormones may affect thermoregulation or stimulate sweat gland activity.

  • Carcinoid syndrome – discussed above.
  • Diabetes insipidus – excessive fluid loss associated with ADH and the kidney’s response to it.
  • Hyperthyroidism – overactivity of the thyroid gland.
  • Menopause – cessation of menstruation associated with low levels of estrogen and progesterone.
  • Pheochromocytoma – discussed above.


  • Antidepressants – used in the treatment of depression and certain mood disorders.
  • Antidiabetic drugs – for managing elevated blood sugar levels in diabetes mellitus.
  • Antipyretics – fever-reducing medication.
  • Hormone replacement therapy (HRT)

Other medication discussed under drug fever may also be responsible for night sweats.

Other Causes

  • Anxiety
  • Endometriosis – presence of endometrial tissue out of the uterus.
  • Head injury
  • Hypoglycemia – low blood sugar levels.
  • Idiopathic hyperhidrosis – excessive sweating for unknown reasons.
  • Night terrors
  • Pregnancy
  • Sleep apnea
  • Spinal cord injury

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