A fever is a temporary increase in your body temperature, often due to an illness. Having a fever is a sign that something out of the ordinary is going on in your body.

For an adult, a fever may be uncomfortable, but usually isn't a cause for concern unless it reaches 103 F (39.4 C) or higher. For infants and toddlers, a slightly elevated temperature may indicate a serious infection.

Fevers generally go away within a few days. A number of over-the-counter medications lower a fever, but sometimes it's better left untreated. Fever seems to play a key role in helping your body fight off a number of infections.

You have a fever when your temperature rises above its normal range. What's normal for you may be a little higher or lower than the average normal temperature of 98.6 F (37 C).

Depending on what's causing your fever, additional fever signs and symptoms may include:

• Sweating
• Chills and shivering
• Headache
• Muscle aches
• Loss of appetite
• Irritability
• Dehydration
• General weakness

Children between the ages of 6 months and 5 years might experience febrile seizures. About a third of the children who have one febrile seizure will have another one, most commonly within the next 12 months.

Taking a temperature

To take a temperature, you can choose from several types of thermometers, including oral, rectal, ear (tympanic) and forehead (temporal artery) thermometers.

Oral and rectal thermometers generally provide the most accurate measurement of core body temperature. Ear or forehead thermometers, although convenient, provide less accurate temperature measurements.

In infants, doctors generally recommend taking a temperature with a rectal thermometer.

When reporting a temperature to your or your child's doctor, give the reading and explain how the temperature was taken.

When to see a doctor

Fevers by themselves may not be a cause for alarm — or a reason to call a doctor. Yet there are some circumstances when you should seek medical advice for your baby, your child or yourself.

Infants

An unexplained fever is greater cause for concern in infants and in children than in adults. Call your baby's doctor if your child is:

• Younger than age 3 months and has a rectal temperature of 100.4 F (38 C) or higher.
• Between ages 3 and 6 months and has a rectal temperature up to 102 F (38.9 C) and seems unusually irritable, lethargic or uncomfortable or has a temperature higher than 102 F (38.9 C).
• Between ages 6 and 24 months and has a rectal temperature higher than 102 F (38.9 C) that lasts longer than one day but shows no other symptoms. If your child also has other signs and symptoms, such as a cold, cough or diarrhea, you might call your child's doctor sooner based on severity.

Children

There's probably no cause for alarm if your child has a fever but is responsive — making eye contact with you and responding to your facial expressions and to your voice — and is drinking fluids and playing.

Call your child's doctor if your child:

• Is listless or irritable, vomits repeatedly, has a severe headache or stomachache, or has any other symptoms causing significant discomfort.
• Has a fever after being left in a hot car. Seek medical care immediately.
• Has a fever that lasts longer than three days.
• Appears listless and has poor eye contact with you.

Ask your child's doctor for guidance in special circumstances, such as a child with immune system problems or with a pre-existing illness.

Adults

Call your doctor if your temperature is 103 F (39.4 C) or higher. Seek immediate medical attention if any of these signs or symptoms accompanies a fever:

• Severe headache
• Unusual skin rash, especially if the rash rapidly worsens
• Unusual sensitivity to bright light
• Stiff neck and pain when you bend your head forward
• Mental confusion
• Persistent vomiting
• Difficulty breathing or chest pain
• Abdominal pain or pain when urinating
• Convulsions or seizures

Fever occurs when an area in your brain called the hypothalamus (hi-poe-THAL-uh-muhs) — also known as your body's "thermostat" — shifts the set point of your normal body temperature upward. When this happens, you may feel chilled and add layers of clothing or wrap up in a blanket, or you may shiver to generate more body heat, eventually resulting in an elevated body temperature.

Normal body temperature varies throughout the day — it's lower in the morning and higher in the late afternoon and evening. Although most people consider 98.6 F (37 C) normal, your body temperature can vary by a degree or more — from about 97 F (36.1 C) to 99 F (37.2 C) — and still be considered normal.

Fever or elevated body temperature might be caused by:

• A virus
• A bacterial infection
• Heat exhaustion
• Certain inflammatory conditions such as rheumatoid arthritis — inflammation of the lining of your joints (synovium)
• A malignant tumor
• Some medications, such as antibiotics and drugs used to treat high blood pressure or seizures
• Some immunizations, such as the diphtheria, tetanus and acellular pertussis (DTaP) or pneumococcal vaccine

Sometimes the cause of a fever can't be identified. If you have a fever for more than three weeks and your doctor isn't able to find the cause after extensive evaluation, the diagnosis may be fever of unknown origin.

Children between the ages of 6 months and 5 years may experience fever-induced convulsions (febrile seizures), which usually involve loss of consciousness and shaking of limbs on both sides of the body. Although alarming for parents, the vast majority of febrile seizures cause no lasting effects.

If a seizure occurs:

• Lay your child on his or her side or stomach on the floor or ground
• Remove any sharp objects that are near your child
• Loosen tight clothing
• Hold your child to prevent injury
• Don't place anything in your child's mouth or try to stop the seizure

Most seizures stop on their own. Take your child to the doctor as soon as possible after the seizure to determine the cause of the fever.

Call for emergency medical assistance if a seizure lasts longer than five minutes.

You may be able to prevent fevers by reducing exposure to infectious diseases. Here are some tips that can help:

• Wash your hands often and teach your children to do the same, especially before eating, after using the toilet, after spending time in a crowd or around someone who's sick, after petting animals, and during travel on public transportation.
• Show your children how to wash their hands thoroughly, covering both the front and back of each hand with soap and rinsing completely under running water.
• Carry hand sanitizer with you for times when you don't have access to soap and water.
• Try to avoid touching your nose, mouth or eyes, as these are the main ways that viruses and bacteria can enter your body and cause infection.
• Cover your mouth when you cough and your nose when you sneeze, and teach your children to do likewise. Whenever possible, turn away from others when coughing or sneezing to avoid passing germs along to them.
• Avoid sharing cups, water bottles and utensils with your child or children.

To evaluate a fever, your doctor may:

• Ask questions about your symptoms and medical history
• Perform a physical exam
• Order tests, such as blood tests or a chest X-ray, as needed, based on your medical history and physical exam

Because a fever can indicate a serious illness in a young infant, especially one 28 days or younger, your baby might be admitted to the hospital for testing and treatment.

For a low-grade fever, your doctor may not recommend treatment to lower your body temperature. These minor fevers may even be helpful in reducing the number of microbes causing your illness.

Over-the-counter medications

In the case of a high fever, or a low fever that's causing discomfort, your doctor may recommend an over-the-counter medication, such as acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin IB, others).

Use these medications according to the label instructions or as recommended by your doctor. Be careful to avoid taking too much. High doses or long-term use of acetaminophen or ibuprofen may cause liver or kidney damage, and acute overdoses can be fatal. If your child's fever remains high after a dose, don't give more medication; call your doctor instead.

Don't give aspirin to children, because it may trigger a rare, but potentially fatal, disorder known as Reye's syndrome.

Prescription medications

Depending on the cause of your fever, your doctor may prescribe an antibiotic, especially if he or she suspects a bacterial infection, such as pneumonia or strep throat.

Antibiotics don't treat viral infections, but there are a few antiviral drugs used to treat certain viral infections. However, the best treatment for most minor illnesses caused by viruses is often rest and plenty of fluids.

Treatment of infants

For infants, especially those younger than 28 days, your baby might need to be admitted to the hospital for testing and treatment. In babies this young, a fever could indicate a serious infection that requires intravenous (IV) medications and round-the-clock monitoring.

You can try a number of things to make yourself or your child more comfortable during a fever:

• Drink plenty of fluids. Fever can cause fluid loss and dehydration, so drink water, juices or broth. For a child under age 1, use an oral rehydration solution such as Pedialyte. These solutions contain water and salts proportioned to replenish fluids and electrolytes. Pedialyte ice pops also are available.
• Rest. You need rest to recover, and activity can raise your body temperature.
• Stay cool. Dress in light clothing, keep the room temperature cool and sleep with only a sheet or light blanket.

Your appointment may be with your family doctor, general practitioner or pediatrician. Here's some information to help you get ready for your appointment and know what to expect from the doctor.

What you can do

• Be aware of any pre-appointment restrictions. When you make the appointment, ask if there's anything you need to do in advance.
• Write down information about the fever, such as when it started, how and where you measured it (orally or rectally, for example) and any other symptoms. Note whether you or your child has been around anyone who's been ill.
• Write down key personal information, including possible exposure to anyone who's been ill or recent travel out of the country.
• Make a list of all medications, vitamins and supplements that you or your child is taking.
• Write down questions to ask the doctor.

For a fever, some basic questions to ask your doctor include:

• What's likely causing the fever?
• Could anything else be causing it?
• What kinds of tests are needed?
• What treatment approach do you recommend? Are there any alternatives?
• Is medicine necessary to lower the fever? What are the side effects of such medications?
• Are there any restrictions that I need to follow?
• Is there a generic alternative to the medicine you're prescribing?
• Do you have any printed materials that I can take with me? What websites do you recommend?

Don't hesitate to ask other questions during your appointment as they occur to you.

What to expect from your doctor

Be prepared to answer questions your doctor might ask you, such as:

• When did the symptoms first occur?
• What method did you use to take your or your child's temperature?
• What was the temperature of the environment surrounding you or your child?
• Have you or your child taken any fever-lowering medication?
• What other symptoms are you or your child experiencing? How severe are they?
• Do you or your child have any chronic health conditions?
• What medications do you or your child regularly take?
• Have you or your child been around anyone who's ill?
• Have you or your child recently had surgery?
• Have you or your child recently traveled outside the country?
• What, if anything, seems to improve the symptoms?
• What, if anything, appears to worsen the symptoms?