Infections are caused by microscopic organisms known as pathogens that enter the body, multiply, and interfere with normal functions. For most healthy people, following a few basic principles can go a long way in knowing how to prevent infections and avoid getting sick.
The average body temperature is 98.6° F (37°C). But "normal" body temperature varies from person to person. It also changes during the day, rising a bit after you eat or exercise. Body temperature is often higher in the afternoon than it is when you wake up in the morning. Fever means a body temperature of 100.4° F (38°C) or higher. An infection is the most common cause of fever. Examples include the flu, pneumonia, food poisoning, and bladder infection.