Apr 01, 2015 · Fever means a body temperature of 100.4° F (38°C) or higher. An infection, such as the flu, is the most common cause of fever. Other conditions can also cause a fever. These include diseases that produce inflammation, such as rheumatoid arthritis, reactions to drugs or vaccines, and even certain types of cancers. Fever symptoms. Jun 20, 2016 · If you or someone you're caring for has a fever, follow these steps to break the fever: A healthy adult with a slight fever may feel like they’ve been hit with a Mack truck, but a baby with a Author: Corey Whelan.