Fevers – can’t live with them, can’t live without them. Or at least, that’s the case once you start coming down with one. Understanding what happens inside your body when you have a fever may help you determine whether to treat yours or not.
How a fever works
It seems counterintuitive that you get the shivers when you’re feeling feverish. You’re hot, but you’re also cold? But it all starts to make sense if you take a look at what’s really going on inside.
Our bodies come with a built-in thermostat in the brain’s hypothalamus. Normally, this thermostat is set to around 98 degrees Fahrenheit. If your body dips below this “set point” – say, from wearing short sleeves during a snowstorm – your brain will turn on processes to create and retain heat. Shivering is the most obvious one; its rapid muscle micro-movements generate heat all over your body. On the other hand, if you get too warm, you’ll start sweating. Sweat evaporating off of your skin cools you down. This happens involuntarily, and your brain is really good at keeping your body’s temperature stable.
What’s going on when you get a fever? Fever is a sign of inflammation in your body. An inflammatory response can be triggered by infection, such as a flu virus, or by immune-related diseases, cancer, or even drugs and alcohol. Certain chemicals released during inflammation turn your body’s thermostat up past 98 degrees.
So now your body is 98 degrees, but your thermostat is at (for example) 102. Your brain thinks your body is too cold, so you shiver to warm up. This is how you can have a fever and feel warm on the outside but get the chills and feel cold inside. Once you warm all the way up to your body’s new set point, you’ll feel warm to the touch, but internally your body will feel just right, so you’ll stop shivering.
A fever “breaks” when your body fights off the bug and the inflammation starts calming down. Your thermostat gets reset back to 98 degrees, but your body is still up at 102. Your brain turns on sweating and sends blood near the surface of your skin to release heat, and you cool back down to your normal body temperature.
The thermostat hypothesis explains how fever medications work. Acetaminophen, aspirin, and NSAIDs such as ibuprofen are fever reducers. Among other effects on the body, they inhibit production of prostaglandins, the chemicals that turn up the thermostat in your brain. During a fever, taking one of these medications will turn your thermostat down a notch.
The benefit of fevers
It’s true that fevers wear you down in a number of ways. They put stress on your body, your heart beats faster, you consume oxygen more quickly, and your cells consume more energy than usual. Very high temperatures (above 105 degrees) can directly damage cells.
However, fevers show up consistently across species as a response to infection, indicating an evolutionary advantage. Even cold-blooded animals that can’t internally regulate their temperature move to a warm rock when they get sick.
A higher body temperature creates an inhospitable environment for many invading bugs to grow and replicate. For example, high temperatures reduce iron levels in the blood, and bacteria have trouble reproducing. Fevers also appear to boost the immune system to fight off infection. So you feel terrible, but you’re actually in a stronger position to beat the bug.
On a population level, there’s even evidence that suppressing fevers with antipyretics leads to increased transmission of the flu virus and, therefore, more cases of the flu and more flu-related deaths.
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So should you treat a fever?
While a fever is a sign of infection, it may also be part of the cure. The idea that any fever must be treated immediately with a reducer could be wrong in many cases. Fever reducers treat a symptom, not the cause of an illness, and lowering your temperature may get in the way of your body’s normal defenses and actually prolong the sickness.
Generally, a fever on its own isn’t dangerous and there’s no real need to treat it. You should, however, seek treatment for the following reasons:
- Infants under 3 months with a fever above 100.4 degrees
- Infants 3–12 months with a fever above 102.2 degrees
- Very high fever (above 105 degrees)
- Persistent fever (longer than 48–72 hours – more guidelines here)
- Your child is unvaccinated
- You have other serious symptoms such as shortness of breath, abdominal pain, headache that doesn’t go away with over-the-counter pain medication, neck stiffness, redness or swelling in joints or extremities, coughing up blood, bloody diarrhea, recent unexplained weight loss, or unusual fatigue that doesn’t go away
- You are an IV drug user
- You have a known serious illness or are immunosuppressed
Fevers also cause dehydration, especially if it’s associated with vomiting or diarrhea. The most important thing to remember with a fever is to stay hydrated. It’s okay if you don’t feel much like eating (that’s a normal response), but keep drinking water. Kids can drink Pedialyte. If a child urinates less than 3 times or an infant has fewer than 3 wet diapers in 24 hours, they’re already dehydrated and should be seen by a doctor right away.
We tend to be concerned with fevers because of how disastrous we look and feel with one. It’s more productive for you to stay home and rest, avoiding spreading germs to the rest of the office anyway. If your child has a fever and is lethargic (so sleepy that you can’t wake them) or inconsolable (can’t stop crying), you should take them to a doctor immediately.
Doctors typically won’t worry if your child (older than 3 months) has a fever of 101 degrees but is behaving normally (playing, eating, and drinking). If your child has a fever and seems fussy, they’re probably uncomfortable, just as many of us are when we’re sick – but they’re probably not seriously ill. It’s your choice to treat a fever in yourself or your child to alleviate discomfort, but again, there’s no medical need to treat the fever itself. (For kids, use children’s acetaminophen or ibuprofen. Don’t give aspirin to children.)