The short answer
A night sweat means soaking your night clothes and bedding in a cool room. The NHS asks you to see a GP if that happens regularly, or comes with fever, cough or weight loss.
The NHS defines night sweats as sweating so much that your night clothes and bedding are soaking wet, even though where you are sleeping is cool.
The NHS says to see a GP if you have night sweats regularly that wake you or worry you, or if they come with a very high temperature, a cough, diarrhoea, or weight loss for no reason.
The NHS names menopause, anxiety, some medicines, low blood sugar, alcohol or drug use, and hyperhidrosis as the most common causes.
NCI lists drenching night sweats and fever for no known reason among Hodgkin lymphoma symptoms, with painless swollen lymph nodes, weight loss over 6 months, itchy skin and heavy tiredness.
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The full explanation.
What counts as a night sweat
Most people sweat at night sometimes. The NHS draws the line in a way that is easy to apply.
It says night sweats are when you sweat so much that your night clothes and bedding are soaking wet, even though where you are sleeping is cool. It also says it is normal to sweat at night if the room or bedding is making you too hot.
So the first question is not how bad it felt. It is whether the room was cool and whether you had to change the sheets.
The reasons that come up first
The NHS lists the most common causes, and none of them are cancer:
- menopause symptoms, often called hot flushes.
- anxiety.
- medicines, such as some antidepressants, steroids and painkillers.
- low blood sugar.
- alcohol or drug use.
- hyperhidrosis, a harmless condition that makes someone sweat too much all the time.
It adds that sometimes the cause of night sweats is never found. Infections, including ones that build slowly, and an overactive thyroid belong on the wider list too.
When the NHS says to book
The advice here is a GP appointment, not an urgent call. The NHS says to see a GP if:
- you have night sweats regularly that wake you up or worry you.
- you also have a very high temperature, or feel hot, cold or shivery, or have a cough or diarrhoea.
- you have night sweats and you are losing weight for no reason.
It notes you will not usually need treatment, but the GP will want to check whether other symptoms are present. If a medicine looks responsible, they may prescribe a different one.
The lymphoma picture
This is why people search this symptom, so it deserves a straight answer.
NCI lists drenching night sweats among Hodgkin lymphoma symptoms. The full list is painless swollen lymph nodes in the neck, underarm or groin, fever for no known reason, drenching night sweats, weight loss for no known reason in the past 6 months, itchy skin especially after bathing or drinking alcohol, and feeling very tired.
Two things stand out. The nodes are painless, which is the opposite of the tender glands you get with a sore throat. And NCI frames these as symptoms that do not go away.
Night sweats on their own, for a fortnight, in someone going through the menopause, is a very different picture from sweats plus a growing painless lump plus months of weight loss.
Sweats during cancer treatment
If you are having treatment, the priority changes, because a fever may mean an infection your body cannot contain.
CDC lists a fever of 100.4 F (38 C) or higher as a sign of infection, along with chills, cough or sore throat, diarrhoea, mouth sores, and redness where a line enters the body. It says to call your health care team if you have signs of an infection, because these can be life threatening and need urgent medical attention.
It also advises talking to your doctor or nurse before taking anything for a fever, since those medicines can hide a more serious problem. Use the 24-hour number your team gave you.
Two weeks of notes
Sweats are hard to describe from memory, and easy to record.
Keep a note by the bed. Mark the nights it happened, whether you changed clothes or bedding, the room temperature, what you drank that evening, and your temperature if you have a thermometer. Add any new medicine.
Bring that page and your medicine list. Symptoms of Cancer explains how patterns like this get weighed.
When to get help sooner
- Call your care team now, and go to an emergency department if you cannot reach them, if you are having cancer treatment and your temperature reaches 100.4 F (38 C) or higher, or chills, a new cough, a sore throat, or redness where a line enters your body come with the sweats. NCI treats these as signs of infection that can be life threatening and need urgent medical attention. Use the 24-hour number your team gave you, and do not sit on it overnight.
- Call your care team within a day or two if you are not on treatment and the sweats keep waking you in a cool room, or they arrive with a cough, diarrhoea, shivering, or weight you did not set out to lose. That is the NHS list for booking a GP appointment.
Sources
Words to know
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Common questions
What actually counts as a night sweat?
The NHS sets a clear bar. Sweating enough that your night clothes and bedding are soaking wet, in a room that is not too hot. Waking up warm under a thick duvet in summer is not the same thing.
Are night sweats a common cancer sign?
They are far more often something else. The NHS names menopause, anxiety, medicines, low blood sugar, alcohol and hyperhidrosis first, and notes the cause is sometimes never found.
What makes them worth reporting sooner?
Company. The NHS list is night sweats with a very high temperature or feeling hot, cold or shivery, with a cough or diarrhoea, or with weight loss for no reason.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
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Your next step
Write down timing, severity, changes, and questions before you talk with a clinician.
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Sources last checked: 2026-08-09 what this meansLast updated: 2026-08-20Next planned review: 2027-07-20
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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