Fever is any body temperature over 100.4°F (38°C). It occurs when your body fights off an infection, disease, or illness, and can often be beneficial. While you can often relieve the symptoms of a fever at home, you should carefully monitor the fever — especially in children, who are at risk of febrile seizure, or convulsions caused by high body temperature. If you or your child have a fever, these are ways you can reduce fever as quickly as possible