As a general rule, the younger your child, the sooner you will need to get him checked out. Here's when the American Academy of Pediatrics recommends you contact your child's doctor:

• Under 3 months: Any fever of 100.4°F or higher, even if he shows no other symptoms of illness. If the fever develops after office hours or on a weekend, go to the emergency room. Young babies have a limited ability to fight illness because their immune system isn't fully developed. Young babies can’t tell you if they are really sick and there are some serious bacterial infections that they are more prone to, like kidney infections, blood stream, and pneumonia.

• 3 to 6 months: A fever of 101°F or higher.

• Over 6 months: A fever 103°F or higher.

• A fever in any age child measuring between 104ºF (40.0ºC) and 105ºF (40.6ºC)

•  Fever in a child over three months of age without an obvious source (accompanied by common cold symptoms, diarrhea, etc)•  Fever more than 3 consecutive days with an obvious source of infection or any fever without an obvious source of infection

• Any fever and sore throat that lasts more than 24 to 48 hours

• You see signs of dehydration, such as a dry mouth, a sunken soft spot, or fewer wet diapers (less than one every 8 hours)

• Your child has a fever and pain when urinating

• Your child is lethargic, refuses to eat, has a rash, or is having difficulty breathing

• Your child has a febrile seizure

• Your child has a fever and has recently returned from a trip abroad

Seek immediate medical help if your child has:

• A fever and is under 3 months old

• A fever of 105ºF (40.6ºC) or higher

• A fever and obvious breathing difficulties

• A fever and is having trouble swallowing to the point where she is drooling because she is unable to swallow her own saliva

• A fever and is still lethargic or listless even after taking fever-reducing medication

• A fever accompanied with a headache, stiff neck, or purplish patches or tiny red spots on the skin

• A fever and severe pain

• A febrile seizure lasting 15 minutes or more

• A febrile seizure and he's having trouble breathing afterwards

• A fever and has compromised immunity (i.e. if the child is on chemotherapy for cancer)