A fever is an increase in the normal body temperature. It is not an illness itself, but rather an indicator of infection or foreign substance in the body like viruses, bacteria, drugs or toxins. A fever is usually a beneficial response as it helps to fight the foreign bodies.

Children may also get a fever after receiving vaccinations or while teething.

How to tell if it’s a fever

Usually, we can touch the forehead of a person who has a fever and feel they are warmer than normal. However, this isn’t an accurate way to determine if someone has a fever or not. Be sure to get a reliable thermometer, and check the temperature orally, rectally or under the arm (auxiliary).

When to see the doctor

  • A baby younger than 3 months has a rectal temperature of 100.4 F (38 C) or higher, even if your baby doesn't have other signs or symptoms
  • A baby older than 3 months has a temperature of 102 F (38.9 C) or higher
  • A child younger than age 2 has a fever longer than one day, or a child age 2 or older has a fever longer than three days
  • An adult has a temperature of more than 103 F (39.4 C) or has a fever for more than three days
  • A person who is taking immunosuppressant drugs, or has a serious illness such as cancer, HIV, heart disease or diabetes and has developed a fever.