A fever is a temporary rise in body temperature. It's one part of an overall response from the body's immune system. A fever is usually caused by an infection. For most children and adults, a fever may be uncomfortable. But it usually isn't a cause for concern. For infants, however, even a low fever may mean there's a serious infection. Fevers generally go away within a few days. A number of. Fever in adults: When to worry Infection is a common cause of fever, but other conditions can also bring the heat. Fever is one of the body's most effective ways of fighting infection. It is part of your body's defense against infection-causing germs. Find out about high temperature (fever) in adults including what causes it, how to tell if you have a high temperature and how to treat it. Fever symptoms may include more than just an increase in body temperature. In adults and children, a temperature of 100.4F (38C) or higher marks a fever. In babies, a temperature of 99.5F (37.5C. A fever is the body's way of battling an illness. Here's how to tell if you have a fever, plus what you should do and when you should seek help. Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with body temperature exceeding the normal range caused by an increase in the body's temperature set point in the hypothalamus. [5][6][7][12] There is no single agreed-upon upper limit for normal temperature: sources use values ranging between 37.2 and 38.3 °C (99.0 and 100.9 °F) in humans. [1][7][8. Discover 12 common types of fevers, their symptoms, precautions, and effective treatments to help you stay informed and safeguard your health year-round. A fever is when your body temperature rises higher than normal. Learn more about fevers including what providers consider a real fever. Fever in children: When to worry You should reach out to your pediatrician if your child 6 months to 2 years: Has a fever higher than 102 F for more than 1 day. Has other symptoms, such as a cough. A person has a fever when their temperature is higher than 100°F (38°C). Learn about fever types, symptoms, causes, and treatments in this article.