Medically Reviewed by Jennifer Robinson, MD on May 12, 2020

What a Fever Is

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When you have an illness or infection, your body temperature may rise above its normal range. This is a fever. It could help your body fight back against its cause. But it might make you feel hot and achy, too. If you have a fever, you may not need to see a doctor. But if your child has one, you may need to call or visit.

Normal Temperature?

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Most of us learned that a normal body temperature is 98.6 F. But new research shows that was the norm for people in the 1800s. Today, studies show that people may be slightly cooler, so the norm is anywhere between 97 and 99 F.

Did you know that your temperature changes through the day? You’re at your coolest overnight and warmest in the evening. You may get warmer if you exercise.

Low-Grade Fever

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If your temperature is higher than normal but it’s lower than 100.4 F, your doctor may say that you have a low-grade fever. A mild illness, like a cold or an ear infection, may cause one. Some people may have a low-grade fever after they get a vaccine. If yours doesn’t get back to normal in a few days, ask your doctor if you should pay a visit.

How Fever Affects Your Body

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If you have a fever, you may feel hot and sweaty. You also might shiver because you feel chilled. Weakness, aches, or fatigue could happen. You may have symptoms of the illness that caused the fever, like a cough or sore throat. Food may not sound good. A rotten mood also is possible. Fevers may be a bit more severe for your child. A small percentage of kids have something called a febrile seizure when their body temperature goes up.

Febrile Seizures?

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Up to 4% of children ages 6 months to 5 years may have a seizure with a fever. Their eyes may roll back. They may seem to faint, and their bodies could become stiff. Shaking and twitching are possible too, but they should stop within a minute. Doctors consider febrile seizures harmless. But to be safe, you should let your doctor know if your child has one.

Why You Get a Fever

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Your body may raise its temperature to help you fight off an infection. When your body is hotter, it makes it harder for viruses or bacteria to survive. The fever also tells your immune system to make more white blood cells to join in the fight. So a fever may help protect you, even if it makes you feel worse for a little while.

How to Take a Temperature

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Thermometers can measure your temperature by mouth, ear, armpit, forehead, or rectum. For older kids and adults, the most accurate method is by mouth with an oral digital thermometer. Rectal is best for babies or small children. To take a temperature that way, put petroleum jelly on the thermometer tip, insert it about half an inch into their rectum, and hold the thermometer still until you get the result.

When to Call the Doctor: Babies

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If your baby has a fever of 100.4 F or higher, tell your doctor right away so they can find out if the fever is a sign of something more serious. No matter how high the fever is, reach out if a seizure comes with it. If the seizure lasts for more than 5 minutes, call 911. A low temperature could also mean that your baby is sick, so if theirs drops below 97.7 F, give your pediatrician a call.

When to Call the Doctor: Children

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Talk with your doctor right away if your child’s fever is above 104 F or lasts several days. Also call if the temperature doesn’t drop after you give medicine to lower it, or if the fever is above 102 F after a vaccine. And tell the doctor if your child seems too sleepy, if they don't drink or pee enough, or if they have a febrile seizure for the first time. If the seizure lasts more than 5 minutes, even if it isn't the first, call 911.

When to Call the Doctor: Adults

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If your temperature is 103 F or higher, the fever lasts at least 2 days, or if the number doesn’t drop after you take medicine to lower it, reach out to your doctor's office. You may also want to call if you haven’t drunk enough fluid or peed enough, or you’ve vomited many times and can’t keep down fluids. Go to the emergency room if you have a fever with a bad headache, a stiff neck, a new rash or confusion, or if it’s 105 F or more.

Should You Bring Down a Fever?

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If you or your child feels well enough to eat, sleep, and do things at home (like read or watch TV), you may not need to try to lower a fever, because the fever itself may fight the illness. Studies show that some people in hospitals get better whether their fevers are treated or not. If your child gets febrile seizures, medicine may make them feel better, but it won't make seizures less likely. Still wonder what to do? Ask your doctor.

How to Bring Down a Fever

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Over-the-counter medicines like acetaminophen and ibuprofen may ease a fever in adults and children older than 6 months. If your baby is 3-6 months old and has a low-grade fever, fluids and rest should do the trick, but call the doctor if your baby becomes irritable. Adults can use aspirin, but never give it to children. Lighter clothes may help. A light blanket and drinking cool liquids could also. A lukewarm shower, bath, or sponge bath may also help people cool down.

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