Night sweats happen when your body’s internal thermostat misfires during sleep, triggering a sweating response even when your bedroom isn’t hot. Occasional episodes are usually harmless and tied to something fixable like your sleep environment, a glass of wine, or stress. But recurring, drenching night sweats, especially paired with other symptoms, can signal something worth investigating.
The causes range from the mundane to the medical, and figuring out which category you fall into depends on how severe your sweats are, how often they happen, and what else is going on in your body.
How Your Body Controls Temperature at Night
A small region at the front of your brain acts as your internal thermostat. It contains specialized heat-sensitive neurons that constantly monitor your core temperature using signals from your skin, blood vessels, and organs. When these neurons detect that you’re too warm, they trigger two cooling responses: they widen blood vessels near the skin’s surface and activate your sweat glands.
During sleep, your core body temperature naturally dips. But if something disrupts this process, whether it’s hormones, medication, infection, or an overheated room, those heat-sensitive neurons can overreact and launch a full sweating response while you’re asleep. The result is waking up damp, sometimes soaked, often confused about why.
Your Bedroom May Be Too Warm
Before looking at medical causes, the simplest explanation is worth ruling out. Sleep specialists recommend keeping your bedroom between 60 and 67°F (15 to 19°C). Anything above 70°F is considered too hot for quality sleep and can easily trigger sweating, especially under heavy blankets or synthetic bedding that traps heat. Memory foam mattresses and polyester sheets are common culprits. Switching to breathable fabrics and lowering the thermostat resolves night sweats for many people.
Hormonal Shifts Are the Most Common Medical Cause
For women in their 40s and 50s, hormonal changes around menopause are the leading cause of night sweats. Declining estrogen levels destabilize the brain’s thermostat, narrowing the range of temperatures your body tolerates before triggering a cooling response. This means even a tiny rise in core temperature can set off intense sweating and flushing.
These episodes, called vasomotor symptoms, affect a significant percentage of women during and after menopause. A large international survey found that over 36% of postmenopausal women experienced moderate to severe episodes in the previous month. For many women, these symptoms persist for years, not months. Night sweats can also begin during perimenopause, well before periods stop entirely.
Men aren’t immune. Low testosterone, which becomes more common with age, can cause night sweats through a similar disruption of temperature regulation. Thyroid disorders also belong in this category. An overactive thyroid speeds up your metabolism, producing excess body heat, sensitivity to warmth, and excessive sweating that often worsens at night.
Medications That Trigger Sweating
If your night sweats started around the same time as a new prescription, the medication is a likely suspect. Antidepressants are among the most common offenders. SSRIs alter serotonin levels in the brain, and serotonin plays a direct role in both mood regulation and sweating. Depending on the specific drug, somewhere between 7% and 19% of people taking SSRIs experience excessive sweating as a side effect.
Other medications frequently linked to night sweats include hormone therapies (like tamoxifen), blood pressure drugs, diabetes medications that can cause low blood sugar overnight, and over-the-counter fever reducers like aspirin or acetaminophen as their effects wear off. Steroids and some migraine medications can also be triggers. If you suspect a medication, talk to your prescriber about alternatives rather than stopping on your own.
Alcohol and Caffeine
Alcohol is a reliable night-sweat trigger for two reasons. First, it dilates blood vessels near your skin, which increases heat loss and can activate sweating. Second, as your body metabolizes alcohol overnight, it creates a mild withdrawal effect that stimulates your nervous system. Even moderate drinking, just a couple of glasses of wine with dinner, can be enough to cause sweating a few hours into sleep.
Caffeine consumed in the afternoon or evening can have a similar, if less dramatic, effect. It raises your heart rate and metabolic activity, both of which increase body heat. If you’re trying to pinpoint a lifestyle cause, eliminating alcohol and late-day caffeine for two weeks is a straightforward experiment.
Sleep Apnea Is an Overlooked Cause
Obstructive sleep apnea, a condition where your airway repeatedly collapses during sleep, is strongly linked to night sweats but rarely the first thing people suspect. A study published in the European Respiratory Journal found that 31% of people with untreated sleep apnea reported frequent night sweats (three or more times per week), compared to just 11% of the general population. That’s roughly a threefold increase.
The connection makes sense: each time your airway closes, your body mounts a stress response that spikes heart rate and blood pressure, generating heat. The encouraging finding is that treating the apnea brings sweating rates back down to normal levels. If your night sweats come with loud snoring, gasping during sleep, or daytime exhaustion, sleep apnea is worth investigating with a sleep study.
Infections and Immune Responses
Night sweats are a classic symptom of several infections, particularly those that cause low-grade fevers your body fights hardest at night (when your immune system is naturally more active). Tuberculosis is the textbook example, but the list also includes HIV, heart valve infections (endocarditis), fungal infections, mononucleosis, and abscesses. These conditions generally come with other symptoms like fatigue, fever, cough, or weight loss, not just sweating in isolation.
Even a common viral illness can cause a few nights of sweating as your immune system ramps up its response. The difference is that infection-related sweats typically resolve as the illness clears, while sweats from chronic infections persist for weeks or months.
When Night Sweats Signal Something Serious
The night sweats that concern doctors most are “drenching” sweats, the kind that soak through your pajamas and sheets and force you to change your bedclothes. In the context of lymphoma and other blood cancers, these drenching sweats are classified as “B symptoms,” alongside unexplained fever and unintentional weight loss.
Certain combinations of symptoms raise the index of concern significantly:
- Unexplained weight loss of more than 5% of your body weight over six to twelve months
- Persistent or recurring fevers without an obvious infection
- Swollen lymph nodes that persist longer than four to six weeks, especially if painless
- Easy bruising or unusual bleeding
- Severe fatigue that doesn’t improve with rest
Any of these paired with persistent night sweats warrants a medical evaluation. Your doctor will likely start with blood work to check for signs of infection, thyroid dysfunction, and abnormal blood cell counts. If swollen lymph nodes are present alongside night sweats, a biopsy may be needed to rule out lymphoma or leukemia.
It’s worth noting that serious causes like cancer are relatively rare compared to hormonal, environmental, and medication-related explanations. Most people with recurring night sweats have a treatable or manageable cause. But the pattern matters: isolated episodes that come and go are very different from weeks of drenching sweats that progressively worsen.
Narrowing Down Your Cause
Start by tracking the basics for a couple of weeks. Note your bedroom temperature, what you ate and drank that evening, any medications you took, and how severe the sweating was. This kind of simple log often reveals a pattern, like sweats only occurring on nights you drink alcohol or on nights your thermostat is set higher.
If no lifestyle pattern emerges and your sweats are frequent or worsening, a medical workup can help. Standard initial tests typically include a complete blood count, thyroid function, blood sugar levels, and inflammatory markers. For women in the perimenopausal age range, hormone levels may also be checked. If sleep apnea symptoms are present, a sleep study is the diagnostic standard. The goal is to work from the most common and treatable causes outward, only pursuing more invasive testing if initial results are unrevealing and symptoms are persistent or accompanied by red-flag signs.