Night sweats are repeated episodes of heavy sweating during sleep — enough to leave your nightclothes or sheets damp or soaked, so you may need to change them. A warm bedroom or too many blankets can make anyone sweat; true night sweats happen even when the room is cool. They have many possible causes. In women at midlife the most common is perimenopause and menopause, but an overactive thyroid, infections, low blood sugar, some medicines, and anxiety can all do the same thing. This page covers the red flags to act on first, then lists the possible causes neutrally.
When to see a doctor
Most night sweats are not an emergency, but seek care the same day, or call emergency services, if sweats come with any of these:
- A high fever, shaking chills, a stiff neck, confusion, or feeling very unwell
- Coughing up blood, chest pain, or severe breathlessness
- Signs of very low blood sugar in someone on diabetes medicine — shakiness, a pounding heart, confusion, or trouble waking
Book a routine appointment if night sweats:
- Happen regularly and wake you or worry you
- Come with unexplained weight loss, swollen glands, or a persistent cough
- Are drenching most nights, or do not settle over a few weeks
These "get it checked" features matter because a few causes — some infections, thyroid disease, and, rarely, blood cancers such as lymphoma — need testing rather than reassurance. A clinician can sort common from serious quickly.
Possible causes
Treat the list below as possibilities to discuss, not a diagnosis. Several can overlap.
Perimenopause and menopause
Falling and fluctuating estrogen triggers hot flashes and their nighttime version, night sweats (together called vasomotor symptoms). They affect most women and can begin years before periods stop, during perimenopause. If you also have irregular periods and sleep or mood changes, this cause is likely — see menopause stages.
An overactive thyroid (hyperthyroidism)
Too much thyroid hormone speeds the body up, causing sweating, heat intolerance, a fast or pounding heart, weight loss, tremor, and anxiety. A simple TSH blood test is the key check — see thyroid health and what to look for in a thyroid test.
Infections
Infections — from a simple viral illness to tuberculosis, among others — often cause fever and sweats. Sweats that come with fever, a lasting cough, or feeling unwell deserve prompt review.
Low blood sugar (hypoglycemia)
A drop in blood glucose overnight can cause sweating heavy enough to dampen pajamas or sheets. This is most relevant for people taking insulin or certain diabetes tablets (such as sulfonylureas). Never adjust diabetes medicine on your own — ask your clinician, who may check your HbA1c and glucose pattern.
Certain medicines
Some medicines list night sweats as a side effect, including some antidepressants, steroids, hormone treatments, and some pain relievers. Do not stop a prescribed medicine because of sweats — raise it with the prescriber.
Anxiety and stress
Anxiety, panic, and ongoing stress can trigger night sweats, often alongside a racing mind or a pounding heart. See stress and cortisol.
Less common causes
Less often, night sweats stem from other conditions — including some blood cancers (lymphoma, leukemia), other hormone problems, obstructive sleep apnea, alcohol use, or a tendency to sweat excessively (hyperhidrosis). These are much rarer, which is why the red flags above matter.
Simple checks a clinician can do
Because several common causes share the same symptom, a short set of tests often points the way. High-yield checks include a thyroid (TSH) test, blood glucose or HbA1c, and — if you are also tired — ferritin to look for low iron (see at-home ferritin testing). A full blood count and a review of your current medicines round it out. Tracking your pattern helps: our symptom score and doctor report can turn what you notice into notes you can hand over.
Possible cause vs typical clues
| Possible cause | Typical clues to discuss |
|---|---|
| Perimenopause / menopause | Age 40s–50s, irregular or stopped periods, daytime hot flashes, sleep and mood changes |
| Overactive thyroid | Heat intolerance, fast or pounding heart, tremor, weight loss, anxiety |
| Infection | Fever, chills, cough, feeling unwell, a recent illness |
| Low blood sugar | On insulin or diabetes tablets; shakiness, hunger, confusion that eases after eating |
| Medicine side effect | Started or changed a drug recently (e.g. some antidepressants or steroids) |
| Anxiety / stress | Racing thoughts, palpitations, sweats linked to worry or panic |
| Less common (e.g. lymphoma) | Drenching sweats plus unexplained weight loss, swollen glands, or persistent fever |
Night sweats usually have an everyday explanation, and at midlife menopause tops the list. Still, because a few causes need timely testing, it is worth mentioning drenching or persistent night sweats to your clinician — especially alongside fever, weight loss, or a new medicine — so the right cause is found. This article is for general information and is not a substitute for personal medical advice; talk to your clinician about what fits your situation.