Sweating during sleep has a wide range of causes, from a bedroom that’s too warm to hormonal shifts, medications, and underlying infections. Most cases are harmless and tied to your sleep environment or temporary stress. But when night sweats are drenching, recurrent, and paired with other symptoms like unexplained weight loss or fever, they can signal something that needs medical attention.
Your Sleep Environment May Be the Simplest Explanation
Before looking at medical causes, it’s worth ruling out the obvious. Your body temperature naturally dips during sleep, and anything that interferes with that cooling process can trigger sweating. Heavy blankets, memory foam mattresses that trap heat, synthetic pajamas, and a warm room are common culprits.
Sleep experts recommend keeping your bedroom between 60 and 67°F (15 to 19°C) for optimal sleep. If your room regularly runs warmer than that, or you’re layering thick bedding, the fix may be as simple as adjusting your thermostat, switching to breathable fabrics, or using a lighter comforter. Alcohol and spicy food close to bedtime can also raise your core temperature enough to cause sweating overnight.
Hormonal Changes and Your Internal Thermostat
Hormonal fluctuations are one of the most common medical causes of night sweats, especially during perimenopause and menopause. Shifting estrogen levels interfere with the hypothalamus, the part of your brain that acts as your body’s thermostat. When estrogen drops, the hypothalamus essentially misreads your body temperature, perceiving heat that isn’t there. It responds by triggering a flush of warmth across your face, neck, and chest, followed by sweating as your body tries to cool itself down.
These episodes, often called hot flashes when they happen during the day, can be intense enough at night to soak through sheets. They typically begin during perimenopause and can persist for several years. Other hormonal conditions can produce similar effects. An overactive thyroid gland speeds up your metabolism and raises body temperature, making nighttime sweating a frequent early symptom. Low blood sugar overnight, which sometimes occurs in people with diabetes, also triggers a sweating response as the body releases stress hormones to raise glucose levels back up.
Medications That Cause Night Sweats
Certain prescription drugs are well-known triggers. Antidepressants are among the most common offenders: up to 20% of people taking them experience excessive sweating, including at night. This applies to several classes of antidepressants, not just one specific type. The sweating tends to start within the first few weeks of treatment and, for some people, persists as long as they take the medication.
Other drug categories linked to night sweats include hormone-blocking therapies used in cancer treatment, steroids, medications for diabetes that can cause blood sugar dips overnight, and some blood pressure drugs. If your night sweats started around the same time you began a new medication, that connection is worth exploring with your prescriber. Adjusting the dose or switching to a different drug often resolves the problem.
Sleep Apnea and Nighttime Sweating
Obstructive sleep apnea, a condition where the airway repeatedly collapses during sleep, is an underrecognized cause of night sweats. Research published in the European Respiratory Journal found that 31% of people with untreated sleep apnea reported frequent nighttime sweating (three or more times per week), compared to just 11% of the general population. That’s roughly a threefold increase.
The mechanism likely involves the body’s stress response. Each time breathing stops, oxygen levels drop and the nervous system kicks into high gear to restart breathing. That surge of adrenaline raises heart rate and can trigger sweating. If you snore heavily, wake up gasping, or feel exhausted despite a full night of sleep, sleep apnea may be driving your night sweats. Treating the apnea, usually with a device that keeps the airway open during sleep, often resolves the sweating as well.
Infections and Inflammatory Conditions
Night sweats are a hallmark symptom of certain infections, particularly tuberculosis, HIV, and infections of the heart valves (endocarditis). The sweating happens because of how your immune system fights these infections. Your body releases inflammatory signaling molecules that temporarily reset your internal thermostat to a higher set point, producing chills and raising your core temperature. When those signals subside, often in waves overnight, the thermostat resets back to normal and your body dumps the excess heat through sweating.
This cycle of temperature spiking and then breaking explains why night sweats from infections tend to feel different from simply being too warm. They’re often drenching, soaking through clothing and bedding, and they come on suddenly. Autoimmune conditions, where the immune system attacks the body’s own tissues, can produce the same pattern of inflammatory sweating.
Cancers Associated With Night Sweats
Night sweats are one of the classic early symptoms of certain blood cancers, particularly Hodgkin lymphoma, non-Hodgkin lymphoma, and leukemia. The same inflammatory mechanism at work in infections applies here: cancer cells produce signaling molecules that disrupt temperature regulation. In lymphoma specifically, drenching night sweats are considered one of the “B symptoms,” a cluster that also includes unexplained fever and significant weight loss.
This doesn’t mean night sweats should make you assume cancer. The vast majority of people who sweat at night have a far more benign explanation. But cancer-related night sweats tend to have a distinct pattern: they’re persistent (not just occasional), severe enough to require changing sheets, and accompanied by at least one other unexplained symptom.
When Night Sweats Need Medical Evaluation
Occasional sweating during sleep, especially when your room is warm or you’ve had alcohol, rarely warrants concern. The red flags that suggest an underlying medical cause are:
- Fever accompanying the sweats
- Unexplained weight loss without changes in diet or exercise
- Decreased appetite that persists
- Swollen lymph nodes in your neck, armpits, or groin
- New rash that appeared around the same time
If any of these apply, a doctor will typically start with blood work looking for signs of inflammation or infection, including markers like C-reactive protein, white blood cell counts, thyroid function, and sometimes a chest X-ray. The goal of initial testing is to look for evidence of systemic inflammation or an abnormality that points toward a specific diagnosis, rather than running every possible test at once.
For night sweats without red flags, the evaluation is less urgent but still worthwhile if the sweating is frequent, disruptive, or new. Keeping a brief log of how often the episodes happen, how severe they are, and whether anything seems to trigger them gives your doctor useful information to narrow the possibilities quickly.