Excessive sweating at night, sometimes called sleep hyperhidrosis, can range from mild dampness to drenching episodes that force you to change your sheets and pajamas. The causes span a wide spectrum, from a bedroom that’s simply too warm to hormonal shifts, medication side effects, infections, and occasionally something more serious like lymphoma. True night sweats happen even when your sleeping environment is cool and your bedding is light, which separates them from ordinary overheating.
Overheating vs. True Night Sweats
Before assuming something medical is going on, it’s worth ruling out the obvious. A warm room, heavy blankets, or synthetic pajamas that trap heat can all make you sweat at night without any underlying condition. This kind of sweating stops when you adjust your environment.
True night sweats are different. They happen regardless of room temperature or how many blankets you’re using. At the more severe end, they soak through your clothes and sheets. If that’s happening repeatedly, something beyond your thermostat is likely involved.
Hormonal Changes
Hormonal shifts are one of the most common drivers of night sweats. Menopause is the classic example. Falling estrogen levels disrupt the body’s internal thermostat (located in a small brain region that regulates temperature), making it overreact to tiny changes in body heat. The result is a sudden hot flash that triggers sweating, often intense enough to wake you up. These episodes can begin during perimenopause, sometimes years before periods fully stop, and may continue for several years afterward.
An overactive thyroid is another hormonal cause. When the thyroid produces too much hormone, your metabolism speeds up, raising your baseline body temperature and making you sweat more easily, both day and night. Low testosterone in men (male hypogonadism) can also trigger night sweats through a similar disruption of temperature regulation. Diabetes, both from blood sugar fluctuations and from the medications used to treat it, is another endocrine-related cause that often gets overlooked.
Medications
Several common medications list excessive sweating as a side effect, and it often shows up most noticeably at night. Antidepressants are among the biggest culprits. Somewhere between 7% and 19% of people taking SSRIs (a widely prescribed class of antidepressants) experience increased sweating, depending on the specific drug. Other classes of antidepressants carry similar risks.
Hormone-blocking therapies used in breast and prostate cancer treatment frequently cause night sweats by inducing a state similar to menopause. Fever-reducing medications like aspirin and acetaminophen can paradoxically trigger rebound sweating as they wear off. Steroids, diabetes medications that lower blood sugar, and some blood pressure drugs round out the list. If your night sweats started around the same time as a new prescription, that connection is worth exploring with whoever prescribed it.
Infections
Chronic and serious infections are a well-known cause of night sweats. Tuberculosis is the textbook example. Active TB typically causes a persistent cough lasting three weeks or longer, chest pain, fatigue, weight loss, fever, and drenching night sweats. The sweating is thought to be driven by the immune system’s sustained inflammatory response, which resets the body’s temperature set point, similar to what happens with a fever.
Other infections linked to night sweats include endocarditis (an infection of the heart’s inner lining), HIV, brucellosis, and various fungal infections. In most of these cases, night sweats don’t appear in isolation. They come alongside other symptoms like prolonged fever, unexplained weight loss, or fatigue that doesn’t improve with rest.
Sleep Apnea
Obstructive sleep apnea is an underappreciated cause of night sweats. When your airway repeatedly collapses during sleep, your blood oxygen drops. Each time this happens, your body jolts itself partially awake to resume breathing. These frequent awakenings and the physical effort of restarting breathing increase activity in the branch of your nervous system responsible for the “fight or flight” response. That heightened state drives sweating.
If your night sweats come with loud snoring, gasping during sleep, or daytime fatigue that doesn’t match how many hours you slept, sleep apnea is worth investigating. Treating the apnea often resolves the sweating.
Anxiety and Stress
The same stress-response system activated by sleep apnea can also be triggered by anxiety. People with generalized anxiety, panic disorder, or post-traumatic stress often experience night sweats because their nervous system stays in a heightened state even during sleep. Nightmares or disturbed sleep architecture keep the body on alert, and sweating is one of the physical consequences. Psychiatric conditions are actually listed among the recognized diagnostic categories for persistent night sweats in clinical guidelines.
Cancer and Other Serious Causes
Night sweats can be an early symptom of certain cancers, particularly lymphomas (both Hodgkin and non-Hodgkin), leukemia, and some rare tumors. In lymphoma, night sweats are part of what clinicians call “B symptoms,” a specific cluster that also includes unexplained fever and losing more than 10% of body weight over six months. The sweating in these cases tends to be severe: the National Cancer Institute defines it as drenching sweats that require changing your bedclothes.
This is the cause people tend to worry about most, and it’s worth putting in context. Cancer is a relatively uncommon explanation for night sweats compared to hormonal changes, medications, or infections. The pattern that raises concern is drenching sweats that persist for weeks, combined with unexplained weight loss, persistent fevers, or swollen lymph nodes. Night sweats alone, without those accompanying signs, are far less likely to point to malignancy.
Less Common Causes
A handful of other conditions can trigger night sweats. Autoimmune disorders, where the immune system attacks the body’s own tissues, sometimes produce chronic low-grade inflammation that leads to sweating. Certain neurological conditions that affect the autonomic nervous system (the part that controls sweating, heart rate, and digestion without conscious input) can also be responsible. A rare adrenal gland tumor called a pheochromocytoma produces surges of adrenaline that cause episodes of sweating, rapid heartbeat, and high blood pressure.
In some cases, no cause is ever found. This is called idiopathic hyperhidrosis, and while it’s frustrating, it generally isn’t dangerous.
What to Pay Attention To
Not all night sweats carry the same weight. A few questions can help you and your doctor narrow things down:
- Severity: Are you damp, or are you soaking through your sheets? Drenching sweats that require changing clothes or bedding are more clinically significant.
- Duration: A few nights of sweating during a cold or flu is normal. Sweating that persists for weeks without an obvious explanation deserves attention.
- Accompanying symptoms: Unexplained weight loss, persistent fevers, fatigue, swollen glands, or a cough that won’t go away all change the picture significantly.
- Timing: Night sweats that started shortly after beginning a new medication point toward a drug side effect. Sweats that coincide with irregular periods suggest a hormonal cause.
Practical Steps to Reduce Night Sweats
While sorting out the underlying cause, a few adjustments can make nights more comfortable. Keep your bedroom cool, ideally between 60 and 67°F (15 to 19°C). Choose breathable, moisture-wicking fabrics for both pajamas and sheets. Cotton and bamboo tend to perform better than polyester or flannel. Avoid alcohol, spicy food, and caffeine in the hours before bed, as all three can raise your core temperature or stimulate your nervous system.
If menopause is the cause, layering lighter blankets instead of one heavy comforter gives you more control. Keeping a cold glass of water by the bed and using a fan can also help you cool down faster when an episode hits. For medication-related sweating, your prescriber may be able to adjust the dose or switch to an alternative with a lower risk of this side effect.