Night sweats happen when your body’s internal thermostat malfunctions during sleep, triggering a sweating response even when your bedroom is cool. The causes range from completely harmless to medically significant, and understanding the pattern of your sweats, along with any other symptoms, is what separates a minor annoyance from something worth investigating.
How Your Body’s Thermostat Triggers Sweating
Your brain has a temperature control center that works like a thermostat with a set point. When your core body temperature rises above that set point, this region activates your sympathetic nervous system, which sends signals down through your brainstem and spinal cord to the sweat glands distributed across your skin. Blood vessels near the surface dilate, sweat glands kick in, and your body cools itself down.
During sleep, this system can be disrupted in several ways. Hormonal shifts, infections, medications, and other conditions can all either raise your core temperature or lower the thermostat’s set point, fooling your brain into launching a full cooling response when none is needed. The result is waking up drenched, sometimes enough to soak through your sheets.
Hormonal Changes and Menopause
The most common cause of night sweats in women is the hormonal shift surrounding menopause. Up to 80% of women experience hot flashes or night sweats at some point during the menopause transition, according to a large, diverse U.S. study. Each episode typically lasts between one and five minutes, often accompanied by chills and anxiety as the body overcorrects after the initial heat surge.
These episodes happen because declining estrogen levels destabilize the brain’s temperature control center, narrowing the range of temperatures your body tolerates before triggering a cooling response. A tiny increase in core temperature that your body would normally ignore instead sets off full-blown sweating and flushing. Night sweats tied to menopause can begin years before periods stop entirely, during the phase known as perimenopause, and may persist for several years afterward.
Medications That Cause Night Sweats
Antidepressants are one of the most overlooked causes. People taking SSRIs (a common class of antidepressants) are roughly three times more likely to report night sweats than people not taking them. In one primary care study, about 9% of patients on these medications experienced the problem. The sweating happens because these drugs increase levels of a brain chemical that interferes with temperature regulation.
Other medications commonly linked to night sweats include:
- Hormone therapy drugs, including those used for breast or prostate cancer
- Blood sugar medications, which can cause low blood sugar overnight, triggering sweating
- Fever reducers like aspirin or acetaminophen, which can cause rebound sweating as they wear off
- Steroids such as prednisone
If your night sweats started around the same time as a new medication, that connection is worth raising with whoever prescribed it. A dose adjustment or switch to a different drug often resolves the issue.
Infections
Night sweats are a classic symptom of several infections, particularly ones that are chronic or slow-burning. Tuberculosis is the textbook example. The bacteria trigger an immune response that ramps up overnight, raising body temperature and causing drenching sweats. Other infections known to cause night sweats include HIV, endocarditis (an infection of the heart’s inner lining), bone infections, and fungal infections like valley fever.
The key difference between infection-related night sweats and other causes is that they almost always come with additional symptoms: fever, unexplained weight loss, fatigue, or a cough that won’t go away. Night sweats from infection tend to be persistent rather than occasional, and they don’t improve with simple changes like cooling your bedroom.
Lymphoma and Other Cancers
Night sweats are one of the hallmark warning signs of lymphoma, both Hodgkin and non-Hodgkin types. In cancer staging, “drenching night sweats” have a specific clinical definition: sweats severe enough that you need to change your bedclothes. This level of severity, combined with unexplained weight loss of more than 10% of body weight and recurring fevers, forms what oncologists call “B symptoms,” which influence how aggressively the cancer is treated.
Lymphoma is not the only cancer associated with night sweats, but it’s the one where sweating is most prominently featured as a diagnostic clue. Other blood cancers, including leukemia, can produce similar symptoms. The sweats in these cases are driven by the immune system’s response to abnormal cells and the inflammatory chemicals they release, which disrupt the brain’s temperature set point.
To be clear, most people with night sweats do not have cancer. But persistent drenching sweats that occur alongside unexplained weight loss or swollen lymph nodes warrant prompt evaluation.
Thyroid and Adrenal Gland Problems
An overactive thyroid revs up your metabolism, producing excess heat that your body then tries to shed through sweating. People with hyperthyroidism often sweat throughout the day, but it can be more noticeable at night. Other signs include anxiety, unexplained weight loss, trembling hands, diarrhea, and a racing heartbeat.
A rarer but more dramatic cause is a pheochromocytoma, a tumor of the adrenal gland that produces surges of adrenaline-like hormones. These episodes cause sudden sweating, headaches, and wild swings in blood pressure. One distinguishing feature: during a sweating episode caused by this kind of tumor, your hands and feet will feel cold and look pale because the same hormones that trigger the sweating also constrict blood vessels in your extremities.
Sleep Apnea
Obstructive sleep apnea, the condition where your airway repeatedly collapses during sleep, is a surprisingly common and underrecognized cause of night sweats. About 31% of people with sleep apnea report frequent nighttime sweating (three or more times per week), compared to just 11% of the general population. The repeated drops in oxygen and spikes in stress hormones each time breathing stops likely explain the sweating response.
If your night sweats come alongside loud snoring, gasping awake, morning headaches, or daytime exhaustion, sleep apnea is a strong possibility. Treating the apnea, typically with a device that keeps the airway open during sleep, often resolves the sweating as well.
When No Cause Is Found
After infections, hormonal issues, medications, and other conditions are ruled out, a significant number of people are left without a clear explanation. This is called idiopathic night sweats. Doctors reach this diagnosis by exclusion, running blood work that might include a complete blood count, blood sugar levels, and thyroid function tests, then concluding that no underlying disease is driving the sweating.
Idiopathic night sweats are frustrating but generally not dangerous. For some people, practical adjustments make a real difference: sleeping in a cooler room, using moisture-wicking bedding, avoiding alcohol and spicy food in the evening, and managing stress. These won’t fix sweats caused by a medical condition, but they can reduce the frequency and severity when no underlying cause exists.
Patterns That Point to a Cause
Not all night sweats carry the same weight. Occasional sweats after a warm evening or a stressful day are rarely concerning. What matters is the pattern. Sweats that happen most nights, drench your bedding, and persist for weeks deserve attention, especially when they show up alongside other changes in your body.
The combination of symptoms matters more than the sweating alone. Night sweats plus weight loss, fever, or swollen glands suggest infection or malignancy. Night sweats plus a racing heart, tremor, and anxiety point toward thyroid issues. Night sweats plus snoring and daytime fatigue suggest sleep apnea. Night sweats that started after a new prescription suggest a medication side effect. And night sweats in a woman in her 40s or 50s, particularly with irregular periods, are most often hormonal. Identifying the pattern is the fastest route to identifying the cause.