If you have a temperature above your normal temperature but below 100.4 F (38 C), it’s called a low-grade fever. A low-grade fever is mild, and most healthcare providers don’t consider it to be of major medical importance. Normal body temperature is 98.6 F (37 C), but that can vary by 1 to 2 degrees from person to person. Your normal temperature may also be lower in the early morning and higher in late afternoon. You can find your own normal temperature by taking it several times a day for several days—when you’re not sick.

A person’s temperature varies depending on how it’s taken. Check with your child’s healthcare provider to find out what temperature they consider a fever. Some providers say that a child is considered to have a fever if their temperature is 99.5°F (37.5°C) or higher by mouth, 99°F (37.2°C) or higher in the armpit, or 100.4°F (38°C) or higher in the rectum. If you use a thermometer that's put in the ear (tympanic) or held near the forehead (temporal), ask your provider what temperature means a fever on that device. Ask your child's provider for a handout so you'll remember the temperature numbers when your child is ill.

Fever is a common symptom of many other illnesses. Inflammatory illnesses such as lupus can cause fever. Cancer can also cause fever. Examples are cancers of the blood and lymph glands such as leukemia or lymphoma. Many people have a fever for a day or two after major surgery, with no sign of infection. This is called “postoperative fever.” And many medicines can cause a fever, such as pain medicines, diuretics, antiseizure medicines, sedatives, and antihistamines. Heatstroke is a life-threatening condition that happens when a person is exposed to high heat and their temperature goes up and won't go down. It can happen if an adult or child is in a hot car or outside on a hot day with no shade. Other symptoms include hot skin, lack of sweat, and confusion or loss of consciousness. If a person has heatstroke, call 911. Move the person into shade and spray or shower them with water until help arrives.

A febrile seizure is when a child with a fever loses consciousness and their arms and legs shake. A febrile seizure can last a few seconds, a minute or two, or as long as 15 minutes. They happen most often in children ages 6 months to 5 years who have a fever between 100°F (37.8°C) and 102°F (38.9°C). But they can happen with a fever of any level. A febrile seizure is more likely to happen with a temperature that rises quickly. A febrile seizure is most often harmless, and is not a sign of epilepsy. They can run in families. It can be scary if your child has a febrile seizure, but the best thing to do is stay calm and watch your child to help prevent injury. Don’t restrain your child. Instead, make sure they are lying safely on the floor or ground, and gently roll your child on their side. Don’t put anything in your child’s mouth. Get medical attention right away for any child who has a seizure.

A fever of this temperature is considered urgent and could mean a medical emergency. Take your baby to their healthcare provider or to the emergency room right away. Don’t give your child any fever-reducing medicine unless your provider tells you to do so. These medicines can mask symptoms that your provider wants to see to help with a diagnosis.

If your baby is younger than 3 months and has a fever of more than 100.4°F (38°C), you should see your provider right away. Follow your provider's instructions for treating fever or being seen at an emergency room.

If your child has any of these symptoms, seek care for them right away:

• Fever of 104°F (40°C) or higher
• Lethargy. This means your child is limp or unresponsive, or won’t make eye contact or interact with you.
• Irritableness. This goes beyond fussiness. It means that your child can’t be comforted and cries for extended periods of time.
• Stiff neck or pain in the back of the neck along with a high fever. This may mean meningitis. Other symptoms of meningitis include vomiting, headache, and sensitivity to bright lights and loud noises.

These things can raise a person’s body temperature by trapping body heat. Lightweight clothing and lightweight bed coverings are best. These allow body heat to escape and help to not raise a person’s temperature. If a person’s body temperature gets too high, it can cause serious problems. In a child, it may cause a febrile seizure. In children and adults, it can cause damage to the brain and other organs.

Acetaminophen and ibuprofen can lower a fever in both children and adults. These medicines won’t make an illness that causes fever to go away, but they can help lessen the discomfort of a fever. Talk with your child’s healthcare provider before giving any medicine. You should never give aspirin to a child.

Hot or cold food and drinks can affect the temperature reading in a person’s mouth. You should take your oral temperature at least 20 minutes after you eat or drink anything.

When someone under age 19 with a fever is given aspirin, it can lead to a rare but very serious disease called Reye syndrome. Reye syndrome is a condition that causes pressure in the brain and fat to build up quickly in the liver and other organs. It only follows a viral infection, such a cold, the flu, or chickenpox. Taking aspirin can trigger it. Symptoms include vomiting, lethargy, confusion, convulsions, and loss of consciousness. It can cause coma and even death. Make sure to read all medicine labels to see if they contain aspirin. Look for the words acetylsalicylic acid or salicylate.