Fever in adults: when to worry

Fever is a rise in body temperature caused by the immune system responding to a trigger. Viral illnesses such as the common cold or COVID-19 can cause it, as can bacterial infections including cellulitis or acute bronchitis. The temperature alone does not identify the cause; your other symptoms, medical history, and how quickly you are changing matter too.

A thermometer reading can be useful, but chills, sweating, weakness, headache, cough, sore throat, rash, or urinary symptoms may give a clinician more context. Fever in an adult who is pregnant, immunocompromised, elderly, or managing a serious long-term condition deserves a lower threshold for advice.

Rest, drink fluids regularly, and choose light clothing and bedding. Check your temperature with the same thermometer and method when you reassess it, and record when symptoms began and any medicine taken. Follow the label or a clinician's directions for fever medicine; do not combine products that contain the same ingredient.

Stay home from close contact while you feel unwell, especially if you have respiratory symptoms. Avoid alcohol if you are dehydrated. Do not use ice baths or extreme cooling, which can trigger shivering and make you feel worse.

Seek emergency help for difficulty breathing, new confusion, fainting, a seizure, blue or grey lips, severe headache with a stiff neck, or a widespread purple or blistering rash. Get urgent medical advice when you cannot keep fluids down, are passing very little urine, have severe localized pain, or are deteriorating rather than recovering.

Arrange clinical advice if fever persists, repeatedly returns, or occurs after recent travel, surgery, or a procedure. A fever with a painful red swollen area may point to cellulitis; fever with a cough or breathing symptoms can occur with acute bronchitis or COVID-19. These patterns need assessment rather than self-diagnosis.

Ask which causes fit your symptoms, how often to check your temperature, which medicines are suitable with your health conditions, and what change should prompt re-contact. Mention your temperature record, recent travel, sick contacts, new medicines, and any rash, pain, breathing change, or reduced urine.