Normal body temperature varies by person, age, activity, and time of day.  Your body temperature is usually highest in the evening. The average normal body temperature is 98.6°F (37°C).  It can be raised by physical activity, strong emotion, eating, heavy clothing, medications, high room temperature, and high humidity. This is especially true in children.  Body temperature varies less in adults. However, a woman's menstrual cycle can elevate temperature by one degree or more.  A rectal temperature up to 100.4°F (38°C) may be entirely normal. A rectal temperature of 100.5°F or above should always be considered a fever. Lower values might be a fever, depending on the person.  In children younger than six months of age, the daily variation is small.  In children 6 months to 2 years old, the daily variation is about 1 degree. Daily variations gradually increase to 2 degrees per day by age six. Many infants and children develop high fevers with minor viral illnesses.  Although infections are the most common causes of elevated body temperature, fevers have a long list of other causes, including toxins, cancers, and autoimmune diseases. Everyone gets cranky when they have a fever. This is normal and should be expected.

Anatomy

A fever is not an illness, it is an important part of the body's defense against infection. Far from being an enemy, it is an important part of the body's defense against infection. While a fever signals to us that a battle might be going on in the body, the fever is fighting for the person, not against.  Most bacteria and viruses that cause infections in people thrive best at 98.6°F. Raising the temperature a few degrees can give your body the winning edge. In addition, a fever activates the body's immune system to make more white blood cells, antibodies, and other infection-fighting agents.

Brain damage generally will not occur unless the fever is over 107.6°F (42°C). Many parents also fear that untreated fevers will keep going higher and higher. Untreated fevers caused by infection will seldom go over 105°F unless the child is overdressed, or trapped in a hot place. The body's thermostat, called the hypothalamus, is found in the part of the brain. It will stop the fever from climbing above 106°F. Some parents fear that fevers will cause seizures. For the great majority of children, this is not the case. However, febrile seizures do occur in some children. Once a child is already known to have a high fever, a febrile seizure is unlikely with the current illness. In any event, simple febrile seizures are over in moments with no lasting consequences.

But how high a fever is doesn't tell you much about how sick your child is. A simple cold or other viral infection can sometimes cause a rather high fever (in the 102 to 104 degrees Fahrenheit, or 38.9 to 40 degrees Celsius, range), but doesn't usually indicate a serious problem. And serious infections may cause no fever or even an abnormally low body temperature, especially in young infants.

Because fevers may rise and fall, a child with fever may experience chills, which occur when the body tries to generate additional heat when the body's temperature begins to rise. The child may sweat as the body releases extra heat when the temperature starts to drop.

Sometimes children with a fever may also breathe faster than usual and may have a higher heart rate. You should call your child's doctor if your child is having difficulty breathing, is breathing a lot faster than normal, or continues to breathe fast after the fever comes down.

Causes

The base cause of a fever can be a variety of different things - some of the more common ones are:

• Viral and bacterial infections
• Colds or flu-like illnesses
• Sore throats and strep throat
• Ear infections
• Viral gastroenteritis or bacterial gastroenteritis
• Acute bronchitis
• Infectious mononucleosis
• Urinary tract infections
• Upper respiratory infections (such as tonsillitis, pharyngitis or laryngitis)
• Medications (such as antibiotics, antihistamines, barbiturates, and drugs for high blood pressure)
• Occasionally, more serious problems like pneumonia, appendicitis, tuberculosis, and meningitis
• Fever can occur in infants who are overdressed in hot weather or a hot environment
• Immunizations: Babies and children sometimes get a low-grade fever after getting vaccinated.
• Collagen vascular disease, rheumatoid diseases, and autoimmune disorders
• Juvenile rheumatoid arthritis
• Lupus erythematosus
• Periarteritis nodosa
• AIDS and HIV infection
• Inflammatory bowel disease
• Regional enteritis
• Ulcerative colitis
• Cancer
• Leukemia
• Neuroblastoma
• Hodgkin's disease
• Non-Hodgkin's lymphoma

Treatment

If the fever is mild and no other problems are present, no medical treatment is required. Drink fluids and rest. If a child is playful and comfortable, drinking plenty of fluids, and able to sleep, fever treatment is not likely to help.  Take steps to lower a fever if you or your child is uncomfortable, vomiting, dehydrated, or having difficulty sleeping. The goal is to lower, not eliminate, the fever.

When trying to reduce a fever:

• If your child is fussy or appears uncomfortable, you can give acetaminophen or ibuprofen based on the package recommendations for age or weight. If you don't know the recommended dose or your child is younger than 2 years, call your child's doctor to find out how much you should give. Remember that fever medication will usually temporarily bring a temperature down, but it will not return it to normal - and it won't treat the underlying reason for the fever. (Never give aspirin to a child under 12 due to its association with Reye syndrome, a rare but potentially fatal disease.) Fever medicines come in different concentrations, so always check the instructions on the package. Take acetaminophen every 4-6 hours. It works by turning down the brain's thermostat. Take ibuprofen every 6-8 hours. Like aspirin, it helps fight inflammation at the source of the fever. Sometimes doctors advise you to use both types of medicine. Ibuprofen is not approved for use under 6 months of age.
• DO NOT bundle up someone who has the chills.
• Remove excess clothing or blankets. The environment should be comfortably cool. For example, one layer of lightweight clothing, and one lightweight blanket to sleep. If the room is hot or stuffy, a fan may help.
• A lukewarm bath or sponge bath may help cool someone with a fever. This is especially effective after medication is given -- otherwise the temperature might bounce right back up.
• DO NOT use cold baths or alcohol rubs. These cool the skin, but often make the situation worse by causing shivering, which raises the core body temperature.
• Drink cool liquids, as tolerated. Offer your child plenty of fluids to avoid dehydration - a fever will cause a child to lose fluids more rapidly. Water, soup, ice pops, and flavored gelatin are all good choices. Avoid drinks containing caffeine, including colas and tea, because they can cause your child to pee more.

Heatstroke is a particularly dangerous type of high temperature, because the body is not able to stop the temperature from continuing to rise. It can happen when a child is left in a hot car or when you exercise too strenuously without enough to drink.  If someone has heat exhaustion or heat stroke, remove the person from the heat source. Sponge the person with tepid water. Place ice packs in the armpits, behind the neck, and in the groin. Give fluids if the person is alert. Seek medical attention. If heat illness is causing the fever, medicines may not lower the body temperature and may even be harmful.  Unexplained fevers that continue for days or weeks are referred to by doctors as fevers of undetermined origin. Most are eventually found to be caused by a hidden infection.

Call a doctor right away if:

• A baby less than 90 days old has a rectal temperature of 100.2°F (37.9°C) or higher.
• A baby 3 to 6 months old has a fever of 101°F (38.3°C) or higher.
• A baby 6 to 12 months old has a fever of 103°F (39.4°C) or higher.
• A child under age two years has a fever that lasts longer than 24 to 48 hours.
• A fever lasts longer than 48 to 72 hours in older children and adults.
• Anyone has a fever over 105°F (40.5°C), unless it comes down readily with treatment and the person is comfortable.
• There are other worrisome symptoms. For example, irritability, confusion, difficulty breathing, stiff neck, inability to move an arm or leg, or first-time seizure.
• There are other symptoms that suggest an illness may need to be treated, such as a sore throat, earache, or cough.
• You think you may have incorrectly dosed acetaminophen or ibuprofen.
• Patient refuses fluids or seems too ill to drink adequately or has persistent diarrhea or repeated vomiting or exhibits any signs of dehydration.
• If patient has a specific complaint (i.e., sore throat or earache)
• If patient still has a fever after 24 hours in a child younger than 2 years or 72 hours in a child 2 years or older.
• If patient has recurrent fevers, even if they only last a few hours each night

Seek emergency care if your child shows any of the following signs along with a fever:

• inconsolable crying for several hours
• extreme irritability
• lethargy and difficulty waking
• rash or purple spots that look like bruises on the skin (that were not there before the child got sick)
• blue lips, tongue, and nails
• infant's soft spot on the head seems to be bulging outward
• stiff neck
• severe headache
• limpness and refusal to move
• difficulty breathing that doesn't get better when the nose is cleared
• leaning forward and drooling
• seizure

At the doctor's ...

Your doctor will perform a physical examination, which may include a detailed examination of the skin, eyes, ears, nose, throat, neck, chest, and abdomen to look for the cause of the fever. You may be asked some of the following:

• How long has the fever lasted?
• Is it increasing? Is it increasing rapidly?
• Do you have alternating chills and fever?
• How frequently does it alternate (days, hours)?
• Did it occur within four to six hours after exposure to something that you might be allergic to?
• Does the fever follow an up and down pattern (is it high, then lower, then high) and at what interval?
• Did it develop suddenly?
• Does it go away and then come back again daily?