How Exactly Does Fever Help You Get Better?

You’ve been dealing with sniffles and a sore throat for a day or so, hoping dearly that it’s just a minor bug, when bam! — you’re suddenly shivering, exhausted, and achy all over. You’ve got a fever. Before you go reaching for a fever-reducing drug, though, listen up: It might feel like death, but fever is often what your body needs to fight off that illness once and for all.

It’s Too Darn Hot

Fevers are such good infection fighters that species across the animal kingdom get them too. That includes everything from warm-blooded mammals like cats and dogs to cold-blooded species like lizards and fish, who move to a sunny rock or warmer water to raise their body temperature when they’re sick. But as common as they are, scientists haven’t known all that much about how fevers help you get better until recently.

The part that was best understood was how fevers start. When a virus or bacterium invades your cells, immune cells called macrophages come to your rescue by gobbling up the invader and cleaning up dead cells. They also let the rest of the body know what’s going down by sending out an alert via proteins called cytokines. These messengers travel up the body’s neural superhighway, known as the vagus nerve, making a beeline for both the brain’s pain center and the hypothalamus. That’s the brain region that controls not only temperature but hunger, thirst, sleepiness — all those other things that go haywire when you’re sick.

Once the hypothalamus knows the body is under attack, it sends out signals to stoke the fires of fever. But why? For a long time, people assumed that a higher body temperature makes it harder for bacteria and viruses to thrive, and eventually kills them off. That’s true, but it turns out to be a very small part of fever’s power.

Another soldier in the fight against infection is the lymphocyte or white blood cell. Once macrophages have begun battle, they present pieces of the invader proteins to T-lymphocytes, which use them to target and destroy infection. These cells get a big boost from toasty temperatures. In 2011, researchers found that when mice were injected with a virus then had their body temperatures raised by 2 degrees, their bodies produced more of a specific type of T-cell than those of the mice who stayed at a normal temperature.

Stick With Me and You’ll Go Places

In January, scientists got an even more detailed answer for why fever gives the immune system a boost: It helps more lymphocytes move to the area under attack. In order to get to their destination, lymphocytes have to move out of the lymph node, stick to the blood vessel, and then travel to the infection. Doing that sticking are molecules called integrins, which are expressed on the lymphocyte surface. Integrins are shaped kind of like balloons, with a large, sticky head and a skinny tail that burrows beneath the surface of the lymphocyte.

In a study published in the journal Immunity, researchers found that fever boosts an integrin-supercharging protein called heat shock protein 90 (Hsp 90) in T-lymphocytes. These bind to the integrin tail, sometimes two at a time, helping more integrins cluster on the surface of the lymphocyte and move it more efficiently to the area it’s needed most. The researchers found that this doesn’t just help T-lymphocytes, but all sorts of immune cells. Interestingly, Hsp-90 only kicked in at a temperature of 101.3 degrees Fahrenheit (38.5 degrees Celsius) — the kind of temp that would likely leave you bedridden for the day.

Fever is a valuable tool for keeping your body healthy, which is why you shouldn’t go too hard on the fever meds. Of course, if your fever is very high — 103 degrees Fahrenheit (39.4 Celsius) for adults, lower for children — you should consult a doctor, who may well tell you to take something to reduce it. But if not, maybe ride it out. Just know there’s a war going on inside you, and do what you can to help the good guys win.

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