What to know about a 40°C fever in adults

Fever is the body's response to illness and may occur with viral or bacterial infections, heat-related illness, or other inflammation. The temperature alone does not identify the cause. Symptoms such as cough, painful urination, rash, abdominal pain, severe headache, or a hot and swollen area of skin help a clinician narrow it down.

Check the reading again with a reliable digital thermometer, following its instructions. Note how the temperature was measured, when it began, recent travel or heat exposure, and any medicines already taken.

Arrange prompt medical advice. While waiting, rest in a comfortably cool room, wear light clothing, and take frequent sips of water or oral rehydration fluid. Avoid alcohol and strenuous activity. A pharmacist or clinician can check whether paracetamol is suitable for you and help you follow the package directions; do not combine products that contain the same ingredient.

Do not use ice baths or very cold sponging, which can trigger shivering. Keep track of alertness, breathing, urine output, fluid intake, and whether symptoms are worsening.

Seek emergency care now for confusion, unusual drowsiness, collapse, a seizure, severe trouble breathing, blue or grey lips, a stiff neck, an intense headache, new weakness, persistent chest pain, or a purple rash that does not fade when pressed. Urgent assessment is also appropriate if the fever follows significant heat exposure or the person cannot keep fluids down.

Contact a clinician promptly if urine becomes very dark or infrequent, symptoms keep worsening, or the person is pregnant, immunocompromised, receiving cancer treatment, or taking medicines that suppress immunity.

Ask what may be causing the fever, whether an examination or tests are needed, which fever medicine is safe with your health conditions, how much fluid to aim for, and which changes should trigger emergency care.