Hyperhidrosis (excessive sweating) is often called a "cold sweat" during the day and a "night sweat" at night. It is important to rule out sweating based on warm temperature before assuming hyperhidrosis. If you are waking up sweaty in bed, first make sure the room's temperature and the amount of insulation (clothing, sheets, and blankets) are not excessive. Hyperhidrosis is usually a recurring condition, and no matter what the cause, you should consult your doctor if you wake up drenched with sweat on a regular basis.
Normally, nerves in our skin and other parts of our body let the brain know when the body is getting too warm. The brain may initiate a number of strategies for lowering body temperature, and a common one is for the hypothalamus to stimulate the sweat nerves so the sweat glands will start producing sweat. As sweat accumulates on the skin (and on our clothing), it starts to evaporate. It is the evaporation of the sweat that cools the body. Once the body temperature normalizes, the nerves tell the hypothalamus to turn off the sweat.
There are hundreds of conditions and dozens of drugs that may cause night sweats. Hormones are responsible for many incidences. If you are a woman at or nearing menopause, hot flashes at night can leave you sweating in bed; the culprit here is a drop in estrogen levels. Adrenaline seems to cause night sweats in people who have migraines or night terrors (nightmares with physical thrashing), a sleep disorder that may or may not accompany sleep apnea (breathing interruptions during sleep). For people with diabetes, the drop in insulin levels in the blood can cause night sweats. Other hormone-related causes include hyperthyroidism, pheochromocytoma, and carcinoid syndrome.
Because conditions like anemia, cancer (especially lymphoma), AIDS, and tuberculosis affect our body's immune response, they frequently cause night sweats. Brain injuries can interfere with the function of the hypothalamus and its sweat-production regulation. Strokes and low blood pressure can produce sweating from the loss of blood circulation. Epileptics and people with cerebral palsy often experience night sweats.
Some medications may have side effects that cause flushing or night sweats, including birth-control pills, antidepressants, and anti-anxiety medications. Other medications can only produce night sweats in high doses and in a small percentage of patients. These medications include aspirin, acetaminophen, niacin (vitamin B3), tamoxifen, hydralazine, nitroglycerin, and sildenafil (Viagra).
Your doctor may recommend environmental changes first, including sleeping in cooler air, avoiding alcohol and spicy foods at dinner, and calming yourself with meditation. If you can find a hypnotherapist who is trained in medical hypnosis, you may learn to control the sweating over the course of two or more treatments.
Anticholinergic drugs block the transfer of acetylcholine and may be helpful in reducing hyperhidrosis, but they can produce a large range of side effects, including shaking, dry mouth, vision problems, and increased heart rate. Endoscopic thoracic sympathectomy is a surgery that is sometimes recommended for excessive underarm sweating, but it is common once sweat glands are removed in one area of the body that compensatory sweating increases in other areas.
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