Fever is also known as hyperthermia, pyrexia, or elevated temperature. It describes a body temperature that’s higher than normal. Fever can affect children and adults.

A short-term increase in body temperature can help your body fight off illness. However, a severe fever can be a symptom of a serious condition that requires immediate medical attention.

Recognizing a fever can enable you to get treatment and proper monitoring for it. Normal body temperature is typically around 98.6°F (37°C). However, the normal body temperature for each person can vary slightly.

Normal body temperature may also fluctuate depending on the time of day. It tends to be lower in the morning and higher in the late afternoon and evening.

Other factors, such as your menstrual cycle or intense exercise, can also affect body temperature.

To check you or your child’s temperature, you can use an oral, rectal, or axillary thermometer.

An oral thermometer should be placed under the tongue for three minutes.

You may also use an oral thermometer for an axillary, or armpit, reading. Simply place the thermometer in the armpit and cross your arms or your child’s arms over the chest. Wait four to five minutes before removing the thermometer.

A rectal thermometer may be used for measuring body temperature in infants. To do this:

1. Place a small amount of petroleum jelly on the bulb.
2. Lay your baby on their stomach and gently insert the thermometer about 1 inch into their rectum.
3. Hold the bulb and your baby still for at least three minutes.

In general, a baby has a fever when their body temperature exceeds 100.4°F (38°C). A child has a fever when their temperature exceeds 99.5°F (37.5°C). An adult has a fever when their temperature exceeds 99–99.5°F (37.2–37.5°C).

Fever occurs when a part of the brain called the hypothalamus shifts the set point of your normal body temperature upward. When this happens, you may feel chilled and add layers of clothing, or you may start shivering to generate more body heat. This eventually results in a higher body temperature.

There are numerous different conditions that can trigger a fever. Some possible causes include:

• infections, including the flu and pneumonia
• some immunizations, such as diphtheria or tetanus (in children)
• teething (in infants)
• some inflammatory diseases, including rheumatoid arthritis (RA) and Crohn’s disease
• blood clots
• extreme sunburn
• food poisoning
• some medications, including antibiotics

Depending on the cause of the fever, additional symptoms may include:

• sweating
• shivering
• headache
• muscle aches
• loss of appetite
• dehydration
• general weakness

Care for a fever depends on its severity. A low-grade fever with no other symptoms doesn’t typically require medical treatment. Drinking fluids and resting in bed are usually enough to fight off a fever.

When a fever is accompanied by mild symptoms, such as general discomfort or dehydration, it can be helpful to treat elevated body temperature by:

• making sure the room temperature where the person is resting is comfortable
• taking a regular bath or a sponge bath using lukewarm water
• taking acetaminophen (Tylenol) or ibuprofen (Advil)
• drinking plenty of fluids

A mild fever can typically be treated at home. In some cases, however, a fever can be a symptom of a serious medical condition that requires prompt treatment.

You should take your infant to a doctor if they’re:

• younger than 3 months old and have a temperature exceeding 100.4°F (38°C)
• between 3 and 6 months old, have a temperature over 102°F (38.9°C), and seem unusually irritable, lethargic, or uncomfortable
• between 6 and 24 months old and have a temperature higher than 102°F (38.9°C) that lasts longer than one day

You should take your child to see a doctor if they:

• have a body temperature exceeding 102.2°F (39°C)
• have had a fever for more than three days
• make poor eye contact with you
• seem restless or irritable
• have recently had one or more immunizations
• have a serious medical illness or a compromised immune system
• have recently been in a developing country

You should call your doctor if you:

• have a body temperature exceeding 103°F (39.4°C)
• have had a fever for more than three days
• have a serious medical illness or a compromised immune system
• have recently been in a developing country

You or your child should also see a doctor as soon as possible if a fever is accompanied by any of the following symptoms:

• a severe headache
• throat swelling
• a skin rash, especially if the rash gets worse
• sensitivity to bright light
• a stiff neck and neck pain
• persistent vomiting
• listlessness or irritability
• abdominal pain
• pain when urinating
• muscle weakness
• trouble breathing or chest pain
• confusion

Your doctor will probably perform a physical examination and medical tests. This will help them determine the cause of the fever and an effective course of treatment.

• confusion
• an inability to walk
• trouble breathing
• chest pain
• seizures
• hallucinations
• inconsolable crying (in children)

Limiting exposure to infectious agents is one of the best ways to prevent a fever. Infectious agents often cause body temperature to rise. Here are some tips that can help reduce your exposure:

• Wash your hands often, especially before eating, after using the toilet, and after being around large numbers of people.
• Show your children how to wash their hands properly. Instruct them to cover both the front and back of each hand with soap and rinse thoroughly under warm water.
• Carry hand sanitizer or antibacterial wipes with you. They can come in handy when you don’t have access to soap and water. Find hand sanitizers and antibacterial wipes online.
• Avoid touching your nose, mouth, or eyes. Doing so makes it easier for viruses and bacteria to enter your body and cause infection.
• Cover your mouth when you cough and your nose when you sneeze. Teach your children to do the same.
• Avoid sharing cups, glasses, and eating utensils with other people.