Sweating in your sleep is common and usually harmless, often caused by a warm bedroom, heavy blankets, or alcohol before bed. But when the sweating is severe enough to soak through your clothes or sheets, it crosses into what doctors call sleep hyperhidrosis, and that can signal something worth investigating. The distinction matters: feeling a bit damp on a hot night is normal thermoregulation, while drenching sweats that wake you up and force a change of bedclothes point to something going on inside your body.
Normal Sweating vs. Night Sweats
Your body sweats to cool itself down whenever your core temperature rises above a set range called the thermoneutral zone. During sleep, minor temperature fluctuations are normal, and light sweating can happen without meaning anything at all. An overheated room, synthetic bedding that traps heat, or simply piling on too many covers will make you sweat more, but this isn’t considered true sleep hyperhidrosis.
Clinically significant night sweats are episodes of generalized sweating during sleep that range from moderate all-over dampness to drenching episodes that soak your sheets. If you’re regularly waking up in wet pajamas and it’s not because your thermostat is set to 75°F, that pattern is worth paying attention to.
Hormonal Shifts and Menopause
The most common medical cause of night sweats in women over 40 is the hormonal shift around menopause. When estrogen levels drop, the part of your brain that regulates body temperature becomes more sensitive. Normally, your body tolerates small temperature changes without triggering a sweating or shivering response. In menopausal women, that comfortable range narrows dramatically, so even a tiny rise in core temperature can set off a full sweating episode, complete with flushed skin, a racing heart, and a wave of heat.
These episodes, commonly called hot flashes when they happen during the day and night sweats when they happen during sleep, are driven by a spike in nervous system activity that causes blood vessels near the skin to open wide. This is the body’s attempt to dump heat, even when there isn’t much excess heat to dump. The sweats can happen several times a night, fragment your sleep, and persist for years. Hormone-related night sweats also affect people undergoing treatments that suppress estrogen or testosterone.
Medications That Cause Sweating
Certain medications are well-known triggers. Antidepressants are among the most common culprits, particularly SSRIs and SNRIs. Clinical trials show that 7% to 19% of people taking SSRIs experience excessive sweating as a side effect. This can show up as daytime sweating, nighttime sweating, or both. If your night sweats started around the same time as a new medication, that timing is an important clue. Other drug categories linked to night sweating include fever-reducing medications like aspirin (which can paradoxically cause rebound sweating), blood pressure drugs, and hormone therapies.
Infections and Immune Responses
Night sweats are a hallmark of certain infections, most notably tuberculosis. People with active TB often experience night sweats multiple times per week alongside a persistent cough, weight loss, and low-grade fever. Other chronic infections, including HIV and bacterial infections of the heart valves, can produce similar patterns.
The mechanism is straightforward: your immune system raises your body temperature to fight off pathogens, and sweating is the cooling response that follows each fever spike. With some infections, these temperature cycles happen more prominently at night, which is why you might feel fine during the day but wake up drenched.
Night Sweats and Cancer
Night sweats can be an early symptom of certain cancers, particularly lymphoma. In Hodgkin lymphoma and some non-Hodgkin lymphomas, drenching night sweats are one of three “B symptoms” doctors look for. The other two are unexplained fever above 100.4°F and unexplained weight loss of more than 10% of your body weight within six months. These three symptoms together help doctors assess how aggressive the disease is and guide treatment decisions.
It’s worth emphasizing that cancer is a relatively rare cause of night sweats compared to hormonal changes, medications, or infections. But the pattern is distinctive: the sweats are typically severe (soaking, not just damp), persistent over weeks, and accompanied by at least one of those other symptoms. Unexplained weight loss alongside drenching night sweats is a combination that warrants prompt medical evaluation.
Low Blood Sugar During Sleep
People with diabetes, especially those taking insulin, can experience night sweats triggered by nocturnal hypoglycemia. When blood sugar drops below 70 mg/dL during sleep, the body releases stress hormones to raise glucose levels. One of the side effects of that hormonal surge is sweating. You might also wake up with a headache, feel groggy or confused, or notice that your skin feels hot and clammy. If you’re on insulin and waking up sweaty, checking your blood sugar at the time of the episode (or wearing a continuous glucose monitor) can clarify whether low blood sugar is the cause.
Sleep Apnea and Sweating
Obstructive sleep apnea, where your airway repeatedly collapses during sleep, is an underrecognized cause of night sweats. Research from a large Icelandic study found a clear association between sleep apnea and nocturnal sweating, and objective measurements of sweat output confirmed that untreated sleep apnea patients sweat significantly more during sleep. These patients also had higher blood pressure, and both the sweating and the blood pressure improved with treatment using a breathing device (PAP therapy).
If your night sweats come with loud snoring, gasping awake, or persistent daytime fatigue, sleep apnea is worth considering. It’s especially common in people who are overweight, though it can affect anyone.
Alcohol and Other Lifestyle Triggers
Drinking alcohol before bed is one of the simplest explanations for nighttime sweating. Alcohol increases your heart rate and widens blood vessels in your skin, both of which raise your skin temperature and trigger perspiration. Even moderate amounts can do this, and the effect is stronger in people who drink regularly or heavily. The sweating tends to happen in the first half of the night, as your body metabolizes the alcohol.
Other lifestyle factors that contribute include eating spicy food close to bedtime, exercising late in the evening (which raises core temperature for hours afterward), and sleeping in synthetic fabrics that don’t wick moisture. Caffeine and nicotine are also stimulants that can activate your sweat response.
Thyroid and Other Endocrine Causes
An overactive thyroid gland speeds up your metabolism, raising your core body temperature and causing sweating around the clock, including during sleep. Other endocrine conditions that can cause night sweats include a rare adrenal gland tumor called a pheochromocytoma, which floods the body with adrenaline, and carcinoid syndrome, where certain tumors release chemicals that cause flushing and sweating. These are uncommon but worth mentioning because the sweating they produce is often dramatic and accompanied by other symptoms like rapid heartbeat, anxiety, or facial flushing.
What Patterns to Watch For
Not all night sweats need medical attention, but certain patterns should prompt a visit to your doctor. Frequency matters: sweating that happens most nights for more than two to three weeks is different from an occasional damp night. Severity matters: light moisture is different from waking in soaked sheets. And context matters most of all.
Night sweats paired with unintentional weight loss, persistent fever, a new cough, swollen lymph nodes, or extreme fatigue suggest something that needs investigation. Night sweats that started after a new medication are worth discussing with whoever prescribed it. Night sweats that happen only on hot nights or after drinking are almost always explained by those triggers alone. Keeping a simple log of when the sweats happen, how severe they are, and what you ate, drank, or took that day can help your doctor narrow down the cause quickly.