Night sweats are surprisingly common, affecting anywhere from 10% to 41% of adults depending on the population studied. Most of the time, the cause is something straightforward: your bedroom is too warm, you had alcohol before bed, or a medication is responsible. But persistent, drenching night sweats can occasionally signal something that needs medical attention. Understanding the full range of causes helps you figure out which category you fall into.
How Your Body Controls Temperature During Sleep
Your brain’s thermostat lives in a region called the preoptic hypothalamus, which simultaneously manages sleep onset and body cooling. When warmth receptors in your skin detect rising temperatures, they send signals to this control center, which responds by widening blood vessels near the skin’s surface and ramping down internal heat production. This is why the blood vessels in your hands and feet dilate as you fall asleep. The degree of that dilation is actually one of the best predictors of how quickly you’ll drift off.
Sweating during sleep happens when this cooling system overshoots or gets triggered inappropriately. Your skin is remarkably sensitive during sleep. Temperature shifts as small as 0.4°C (less than 1°F) can alter sleep patterns without any change in core body temperature. So anything that pushes your skin temperature above its narrow comfort window, whether that’s a thick blanket, a warm room, or an internal hormonal surge, can activate your sweat glands while you’re unconscious.
Your Bedroom May Be Too Warm
The simplest explanation is often the right one. Sleep experts recommend keeping your bedroom at about 65°F (18.3°C), which is cooler than most people think. Humidity matters too: the EPA recommends indoor relative humidity between 30% and 50%, and it should never exceed 60%. High humidity prevents sweat from evaporating, trapping heat against your skin and making you feel hotter than the room temperature alone would suggest. Heavy bedding, memory foam mattresses that retain heat, and synthetic sleepwear all compound the problem.
Alcohol and Late-Night Eating
Drinking alcohol before bed is one of the most common and least recognized causes of night sweats. Alcohol causes blood vessels near the skin’s surface to widen, increasing blood flow to the skin and pulling heat away from your core. Your core temperature drops, but your body misreads the situation and tries to correct it by sweating, attempting to shed heat through the skin even though your internal temperature is already falling. It’s an inefficient, counterproductive loop that leaves you damp and uncomfortable.
Eating a large or spicy meal close to bedtime can do something similar, raising your metabolic rate and body temperature during the hours when both should be declining.
Medications That Cause Sweating
If your night sweats started around the time you began a new medication, that’s a strong clue. Antidepressants are among the most common culprits. SSRIs cause excessive sweating in roughly 7% to 19% of people who take them, depending on the specific drug. Clinical trial data puts the range at 3% to 11%. Older tricyclic antidepressants cause it too, as do certain other antidepressants like venlafaxine and bupropion.
Other medications known to trigger night sweats include fever reducers like aspirin and acetaminophen (which can cause rebound sweating as they wear off), blood pressure medications, hormone therapies, and some diabetes drugs. If you suspect a medication is responsible, your doctor can often adjust the dose or switch to an alternative.
Hormonal Changes and Menopause
For women in perimenopause or menopause, night sweats are one of the hallmark symptoms. The mechanism is now fairly well understood. As estrogen levels decline, a group of specialized neurons in the brain’s temperature-regulation center becomes overactive. These neurons project directly into the areas that control heat dissipation, essentially relaying estrogen signals to your body’s cooling system. When estrogen drops, these signals go haywire.
The practical result is that your body’s “thermoneutral zone,” the temperature range in which you neither sweat nor shiver, gets dramatically narrower. In women with hot flashes, the sweating threshold drops, meaning it takes a much smaller rise in body temperature to trigger a full sweat response. A temperature fluctuation that would have gone unnoticed a few years earlier now sets off drenching night sweats. This is why menopausal night sweats can be so intense even when the room temperature hasn’t changed.
Low testosterone in men can produce a similar effect, though it’s less commonly recognized. An early-morning blood test can check for this.
Low Blood Sugar Overnight
If you have diabetes or take blood sugar-lowering medications, nighttime drops in blood sugar can trigger sweating. When glucose falls too low, your body releases adrenaline and related stress hormones to push it back up. That adrenaline surge causes sweating, a rapid heartbeat, trembling, and anxiety. You might wake up drenched and shaky without realizing your blood sugar was the trigger. If this pattern sounds familiar, testing your blood sugar during a typical episode can confirm it.
Sleep Apnea
Obstructive sleep apnea, where your airway repeatedly collapses during sleep, is an underappreciated cause of night sweats. Each time your breathing stops, your body mounts a stress response that can include sweating. If your night sweats come alongside snoring, daytime fatigue, or a partner reporting that you stop breathing during sleep, a sleep study can determine whether apnea is the cause. Treating the apnea often resolves the sweating.
Infections and Immune Conditions
Certain infections are classically associated with night sweats. Tuberculosis, in its reactivated form, typically presents with cough, weight loss, low-grade fever, and night sweats several times per week. HIV infection frequently causes fever with or without night sweats, either from the virus itself or from secondary infections. One such secondary infection in advanced HIV causes fever, weight loss, and drenching sweats as its primary symptoms.
Other infections that can cause night sweats include bacterial endocarditis (an infection of the heart valves), abscesses, and infectious mononucleosis. These are almost always accompanied by other symptoms like fever, weight loss, or general malaise.
When Night Sweats Are a Warning Sign
The night sweats that deserve prompt medical attention are the drenching kind, where you wake to find your pajamas, sheets, and blankets soaking wet. This level of sweating, especially when combined with unexplained weight loss or persistent fevers, is recognized as a potential symptom of lymphoma and other cancers. These are called “B symptoms” in oncology, and they carry specific diagnostic weight.
Other conditions that can cause persistent, unexplained night sweats include hyperthyroidism (an overactive thyroid), pheochromocytoma (a rare adrenal gland tumor), and carcinoid tumors. These are uncommon but worth ruling out when sweats persist without an obvious explanation.
What Doctors Look For
If you bring up persistent night sweats with no obvious cause, the typical initial workup is straightforward and cost-conscious: a complete blood count, thyroid function test, tuberculosis screen, HIV test, a marker of inflammation, and a chest X-ray. These basic tests catch the most common serious causes. If everything comes back normal, further testing depends on the overall picture. A sleep study might be ordered if apnea is suspected. Hormone levels might be checked. In rare cases where a hidden cancer is a concern, imaging of the chest and abdomen or a bone marrow biopsy may follow.
For most people, though, the cause turns out to be something manageable: a warm bedroom, alcohol, a medication side effect, or hormonal shifts. Cooling your sleep environment to 65°F, switching to breathable bedding, cutting back on evening alcohol, and reviewing your medication list with your doctor resolves night sweats for the majority of people who experience them.