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What Causes Night Sweats? 14 Medical Explanations

Could your bed double as a wading pool by morning? Here's what causes night sweats—and when you should see a doctor about them.

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What causes night sweats?

Everyone has tossed off the covers on a too-warm night or woken up with a sheen of sweat after a particularly vivid nightmare. While annoying, sweating during the night consistently typically isn’t a problem. But regularly waking up in drenched sheets and soggy pajamas are symptoms that suggest a medical condition known as sleep hyperhidrosis, or night sweats, according to the Mayo Clinic.

Night sweats are actually relatively common. Research shows that anywhere from 10 to 40 percent of adults report them in a given year. What causes night sweats? Lots of things, which is why there’s no one-size-fits-all solution. To stop PM perspiration, you have to first identify what’s causing your night sweats. Where to start? This list, which includes the common and the relatively rare.

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Thyroid disorders

When you’re wondering what causes night sweats, you have to consider your thyroid—the tiny, butterfly-shaped gland in your neck. It governs how your body uses energy, according to the Mayo Clinic, and when it pumps out too much of the hormone thyroxine into your system (aka hyperthyroidism), it causes your internal engine to rev up. That can lead to night sweats, as well as other symptoms like increased appetite, racing heart, and unintended weight loss. Blood tests can easily identify the condition—here are some more symptoms that indicate you should get your thyroid checked. Usually, the symptoms can be tamed with hormone treatment.

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Low blood sugar

If you have type 1 diabetes, waking up feeling all hot and bothered might be your body’s way of alerting you to low blood sugar, also known as hypoglycemia. This triggers the release of epinephrine (adrenaline), the “fight-or-flight” hormone responsible for making you sweat, according to the American Diabetes Association. Night sweats may occur if you don’t inject the correct amount of insulin right before you hit the sheets, according to the online resource Diabetes Self Management. Fortunately, these bouts of sweat are treatable, as taking preventative measures like eating a late night snack can help even out your insulin levels.

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Anxiety

Stress sweat is different than the type your body pumps out during a workout. When anxiety hits, moisture is released from the apocrine glands in the armpits, groin, and scalp, according to the International Hyperhidrosis Society. (If you’re just overheated, your body releases sweat through other glands as well.) To help an anxious brain turn off at night, try gentle bedtime yoga, deep breathing, or meditation before you climb between the sheets. Focus your mind on feeling relaxed and cool—your sweat glands should get the message. Or repeat one of these phrases that can quell anxiety.

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Infections

Infections can cause night sweats, with tuberculosis being the biggest culprit. Per the CDC, symptoms of TB often include a fever that can lead to night sweats and chills (as well as weight loss, loss of appetite, and a cough that lasts three weeks or more). Other, less common types—including bacterial infections, osteomyelitis (bone inflammation), and endocarditis (heart valve inflammation)—can trigger night sweats, too, notes WebMD.com.

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Menopause

Up to 85 percent of women report hot flashes during menopause, and they don’t just happen during the day. During menopause, estrogen and progesterone—hormones that, among other things, affect the body’s temperature control—fluctuate, causing the characteristic sudden warmth. Keep a fan by the bed and flip it on when you feel flushed, or consider moisture-wicking pajamas like Cool-jams, which are designed to help keep menopausal women dry at night.

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PMS

Younger women can suffer night sweats, too—and the same hormones are to blame. Researchers have noticed that women in their luteal phase (the second half of the menstrual cycle—when PMS symptoms tend to strike—show an increase in sweat production, in comparison to when they were in the first half of the cycle.

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Alcohol

The same glass of wine that may help you relax before bed could lead you to wake up in a pool of sweat. Alcohol can affect the nervous system and the body’s ability to regulate and sense body temperature, according to WebMD. Drinking causes blood vessels in the skin to widen (a process is called vasodilation), leading you to feel toasty and flushed.

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Medications

Certain meds, including antidepressants like SSRIs and diabetes medications such as metformin, can cause your body to heat up between the sheets, according to the Mayo Clinic. Even OTC meds like the pain-killer naproxen can be an issue. The International Hyperhidrosis Society has a comprehensive list of Rx drugs that can make you sweat.

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Sleep apnea

Obstructive sleep apnea, or OSA, is a disorder that causes your throat muscles to relax and interfere with your airway, the Mayo Clinic explains. As a result, your breathing repeatedly stops and starts while you slumber. The increased effort needed to catch your breath can lead you to wake up red-faced and drenched in sweat. One 2013 study found that 30 percent of men and 33 percent of women with OSA reported sweating at night, compared to 9 percent of men and 12 percent of women in the general population.

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Caffeine

Sometimes, what causes night sweats is as simple an answer as your favorite cuppa. Caffeine has its perks, but keeping you dry at night isn’t one of them. Caffeine is a mild stimulant, which means it revs up—and heats—the central nervous system. Menopausal women may be especially susceptible to this: Research has shown that caffeine intake increases the night sweats and hot flashes these women experience. Learn what else happens to your body when you drink that venti latte.

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Low testosterone (Low-T) levels in men

There’s a treatment for prostate cancer that can trigger hot flashes in up to 80 percent of patients. Called androgen deprivation, the treatment reduces levels of the sex hormone testosterone. Although more research is needed, scientists suspect that the thermal control center in the brain’s hypothalamus—part of the nervous system—is responsible, according to the experts at Harvard Health. They theorize that the nervous system sends out signals that cause blood vessels in the skin to widen, producing a warm sensation similar to the hot flashes experienced by menopausal women.

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GERD

There hasn’t been a lot of research on night sweats and the form of heartburn known as gastroesophageal reflux disease (GERD) and night sweats. But at least one 2003 study found an association: The study authors note that informal observations suggest that patients treated for GERD often have dramatic relief of their night sweats. Fortunately, controlling GERD can be as simple as making a few diet changes—here’s where to start.

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Chronic fatigue syndrome

Night sweats often accompany myalgic encephalomyelitis (the medical term for chronic fatigue syndrome), according to the Centers for Disease Control and Prevention. This energy-zapping condition hits an estimated 2.5 million Americans; often night sweats can be signal an early stage of the disease or a relapse, according to The American ME and CFS Society. The society notes that what causes night sweats can be an immune system activation, hormonal imbalances (typically during menopause), and low blood sugar.

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Cancer

Lymphoma is a cancer that attacks the body’s germ-fighting network known as the lymphatic system. One sign of lymphoma can be drenching night sweats, according to the Mayo Clinic. It’s important to note that lymphoma would be accompanied by other symptoms as well—such as fatigue, weight loss, and shortness of breath—so talk to a doctor before contemplating this scary diagnosis. Here are 9 more things your sweat can tell you about your health.

Tracy Middleton
Tracy Middleton is an experienced health and wellness journalist and is passionate about fitness, eating well, and coffee.