Persistent night sweats, particularly when drenching and unexplained, should not be attributed solely to summer heatwaves and could be an early indicator of cancer, according to Dr. Jiri Kubes, a radiation oncologist at the Proton Therapy Centre. While hot weather commonly leads to uncomfortable nights, Kubes emphasizes that continuous sweating should prompt medical attention.
Cancer Research UK reports that about one-third of individuals delay seeking medical advice for six months after noticing warning signs. These signs can include night sweats, fatigue, persistent itching, changes in appetite, and bloating. Although often linked to other health issues or environmental factors, these symptoms can also be associated with serious cancers, and delayed diagnosis can have severe consequences.
"The important distinction is whether there is an obvious explanation," Dr. Kubes stated. He explained that if one is waking up repeatedly with pajamas soaked through in a cool room, it differs from simply feeling clammy during warm weather.
Drenching night sweats are a known symptom of certain blood cancers, such as lymphoma. These cancers arise from DNA changes in blood cells, leading to abnormal cell multiplication that hinders healthy cell function. Over 41,000 people are diagnosed with blood cancer annually in the UK.
While symptoms vary, drenching night sweats, fatigue, and frequent infections are common indicators of blood cancer. Dr. Kubes advises that while one or two sweaty nights during a heatwave are usually not cause for alarm, regularly occurring unexplained night sweats lasting more than two or three weeks warrant a GP appointment. Individuals experiencing severe sweating or accompanied by other concerning symptoms should seek advice sooner.
Other potential cancer symptoms include unexplained bruising, bleeding, bone or joint pain that disrupts sleep or daily activities, unintentional weight loss, shortness of breath, and persistent itchy skin. Painless swelling in the neck, armpit, or groin can also be a cause for concern.
However, Dr. Kubes stressed that cancer is not the most common cause of night sweats. Numerous other factors can contribute, including menopause, anxiety, an overactive thyroid, alcohol consumption, and certain medications like antidepressants, steroids, and some painkillers. Similarly, tiredness is common during heatwaves but becomes more concerning when severe, prolonged, and accompanied by symptoms like drenching sweats, fever, or weight loss.
The UK has experienced its fifth heatwave this year, with the UK Health Security Agency issuing an amber heat health alert warning of a potential rise in deaths due to extreme temperatures. Data indicates that deaths linked to hot weather in May and June of this year nearly doubled the total figure for all of 2025, highlighting the significant health risks posed by very hot weather, particularly for vulnerable populations such as older adults and those with pre-existing medical conditions.