However, fever is not what causes your baby to get sick. In fact, it's a sign that his immune system is working properly to fight off an infection. When bacteria and other germs invade the body, fever stimulates the production of white blood cells and other defenses to destroy the unwanted invaders. Fever can make your baby uncomfortable, but it's seldom harmful. They can also accompany more serious respiratory problems such as croup and pneumonia, urinary tract infections, and many types of viral infections.
Some infants also develop a fever after being vaccinated.
A low fever by itself almost never causes serious harm. In some children, a sharp spike in temperature can trigger seizures called febrile convulsions that may cause them to turn pale, stiffen, twitch uncontrollably, or even lose consciousness. These convulsions typically last one to two minutes, though they can range from a few seconds up to ten minutes. Fortunately, although they're frightening to watch, febrile convulsions are rarely dangerous. If your child has a febrile convulsion, don't restrain him.