 [ Symptoms ] what causes a fever in babies [ Disease ] there can be many causes for a baby is fever dehydration is one or the infant might be over bundled with clothes in a relatively warm environment the rule of thumb is to dress your baby in just one more layer of clothing than you are comfortable in most commonly fever is caused by an infection the body is immune system senses the “foreign invader”   such as bacteria or a virus   and sends a chemical message to the brain is temperature center instructing it to crank up the heat inside the body this has many advantages some bacteria and viruses do not like the higher temperature and are then more easily destroyed by the immune system the higher body temperature helps the body to ward off the infection in this way fever is actually our friend it lets us know that an infection may be brewing and it helps to fight off the infection