Fever in adults is usually caused by an infection, such as a viral or bacterial infection. When the body is trying to kill infectious invaders such as viruses or bacteria, it raises the body temperature to make it harder for these microbes to survive. Other conditions that can cause a fever include heat exhaustion, certain inflammatory conditions such as rheumatoid arthritis, a cancerous tumor, and some medications or vaccines. The hypothalamus, a part of the brain, controls the body temperature and may reset it to a higher temperature in response to an infection, illness, or some other cause.

Depending on whats causing a fever, other fever signs and symptoms may include sweating, chills and shivering, headache, muscle aches, loss of appetite, irritability, dehydration, and general weakness. A very high fever can cause confusion, extreme sleepiness, irritability, and seizures.

To determine the cause of a fever, a doctor may ask about other symptoms such as coughing, abdominal pain, vomiting, diarrhea, or pain when urinating, recent surgeries or injuries, recent vaccinations, new drugs you may be taking, and recent travel, particularly travel abroad. By itself, fever is usually harmless, though a high fever can be miserable. Drinking plenty of fluids to help cool the body and prevent dehydration, eating, wearing loose comfortable clothing, and taking a medicine that reduces fever such as paracetamol can help alleviate the discomfort associated with fever. However, if a fever is accompanied by severe headache, rash, stiff neck, mental confusion, strange behavior or altered speech, persistent vomiting, difficulty breathing or chest pain, abdominal pain, pain when urinating, or convulsions or seizures, immediate medical attention is necessary.