In about 400 BC, Hippocrates said “Give me the power to create a fever, and I shall cure any disease.” Hippocrates knew that fever was a symptom of disease, not the disease itself. It is the body’s response to illness-its defense against infection.

It’s 2400 years later, and I still spend my days telling people that fever is good, we want fever, fever means that our child’s immune system is working… Fever rules!

A normal human oral temperature is between 97.6 and 99.6 degrees Fahrenheit (37.5 – 38.3 Centigrade). Rectal temps are about a degree higher, axillary and ear temps about a degree lower. Temperatures vary by about a degree through the day, increase when you exercise, and vary from person to person.

The most common cause of fever is infection, but there are other causes: illicit drug use (amphetamines and cocaine), medicine side effects, brain trauma, heat stroke, cancer, vaccine reactions, hyperthyroidism, and inflammatory diseases like lupus, rheumatoid arthritis, and irritable bowel disease. Most of the non-infectious causes give a persistent fever, while fever from infection generally gets better after 3-5 days.

Note that teething was not on that list. Teething can increase a baby’s body temp a little, but not to the point of fever.

Pediatricians define fever as a rectal temp above 100.4 F. Random, but it works as a general rule of thumb.

We get fever when a part of the brain called the hypothalamus is triggered by “pyrogens,” which cause release of prostaglandin E2. Prostaglandin E2 resets the hypothalamus to a higher temperature, like the thermostat in a house. This causes peripheral blood vessels to constrict (thus your munchkins cold hands), generation of more heat, and shivering (small muscle constriction to generate even more heat).

Fever works to fight infection in a variety of ways. High temperatures:

• Limit the spread of a virus (like the common cold),  by blocking that virus’s ability to explode the cells in which it has been multiplying to spread further throughout your body.
• Hinder a bacteria (like strep throat)’s ability to divide and make more bacteria.
• White blood cells, the cells that fight infection, move around better with a fever.
• White blood cells also chomp on bacteria better with that high temp (phagocytosis).
• Toxins produced by bacteria don’t work as effectively with a fever.
• T-cells, which also fight infection, proliferate better.

Fever is good.

There are doctors who will tell people that they should never treat a fever. I, however, am in the “treat for comfort” camp. Fever generally makes kids feel tired (not always a bad thing), fussy, and can make them feel cold. It is uncomfortable and can burn off a lot of fluid at a time when we want our children to stay hydrated. A rapid change in temperature in a young child (6 months to about 5 years) can cause a febrile seizure. If your child is miserable, not drinking as much as you would like, or in pain from a sore throat or headache, acetaminophen or ibuprofen will help him or her to feel better.

Brain damage occurs with temperatures above 108 F (42 C), with things like anesthesia reactions and heat stroke. Only in Hollywood do you get brain damage from a common illness with a 104 F  temperature.

Normal childhood viral infections like colds and gastroenteritis generally trigger fevers in the 99 F to 104 F range. Fevers tend to go up a little in the morning, improve during the day, and spike higher at night. That 103 temperature that improves during the day but then spikes at 10 PM is actually pretty reassuring, because that is the classic viral fever curve. Kids generally get better on their own with rest, fluids, and time.

Bacterial infections, like strep throat, pneumonia, or sepsis, are more serious and sometimes need treatment with antibiotics. They classically give fever all day long, rather than in that morning and evening viral pattern. They are accompanied by symptoms specific to the source of the infection, like lethargy, breathing problems, sore throat, earache, or pain with urination.

So, when to worry? Your doc will want to see any baby under 3 months with a fever, because their immune systems are inexperienced at that age. We like to see kids with 104 F temperatures or fevers that persist longer than 3 nights, just to make sure there isn’t anything bad going on. Call us if your munchkin has trouble breathing, lethargy, inconsolable irritability, an earache, or pain with urination. We like to see kids with fever if they have compromised immune systems or serious medical problems. We like to see kids with fever caused by heat stroke rather than infection.

Never throw them into a cool bath or rub them down with alcohol, because fever seizures are caused by a rapid change in temperature, not by the actual height of the temperature. It is safe to give a child a tepid bath about an hour after they have a dose of acetaminophen or ibuprofen, because the medicine will keep the temperature from bouncing back up.

Never give aspirin to kids because it has been linked to Reye’s syndrome.

And if you’re worried, call your pediatrician. It’s what we’re here for.