If your newborn is younger than 2 months with a rectal temperature greater than 100.4 degrees Fahrenheit (38 degrees Celsius), go to an emergency department immediately.

If your baby is between 2 and 3 months old and their temperature (taken any way) is greater than 100.4 degrees Fahrenheit, call your baby’s primary care provider immediately.

If your baby is older than 3 months, call the primary care provider right away if:

• Your child is crying inconsolably.
• Your child is difficult to awaken.
• Your child has been in a very hot place, such as inside a hot car.
• Your child has other symptoms such as a severe headache, stiff neck, or other severe pain.
• Fever is accompanied by a rash.
• Your child is taking steroids or has an immune system problem, such as cancer.
• Your child looks or acts very sick.
• Your child has severe vomiting or diarrhea.
• Your child is not up to date on their vaccines.
• Your child has a seizure (convulsion).

What is a fever?

A fever is formally defined by most primary care providers as a temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) and higher.

Your baby makes a fever to fight off germs. The immune system increases the body temperature to help get rid of germs without causing harm to your child.

A fever often makes your baby feel hot and look flushed. Fevers can cause headaches or body aches, sweating or shivering. Some children get headaches with fever, and most lose their appetites. Some children just feel sleepier than usual. Many babies are cranky when they have fevers and feel much better when their fevers go down again.

You may notice your child’s heart rate and breathing rate increase with fever. This is a normal part of fever.

What causes a fever in a newborn?

Fevers are common in children, but for a newborn baby, a fever can be a sign of a dangerous infection. This is why children under 2 months should be taken to an emergency department in the case of a fever of 100.4 or higher.

Most fevers in children are caused by viruses. A much smaller number are due to bacterial infections, such as ear infections, strep throat or pneumonia.

Prolonged fever, meaning fever for more than a week, or recurring fevers can be a sign of underlying chronic disease, so it is important to check with your child's primary care provider.

Learn more about treating fevers in otherwise healthy children. Watch this video to better understand why children get fevers, and when you should call the primary care provider.