Why Does Your Body Temperature Rise When You Have a Virus Such as the Flu?

man sick in bed
One purpose of a fever is to raise the body's temperature enough to kill off certain viruses sensitive to temperature changes, like the flu. Uwe Krejci/Getty Images

When your body temperature rises because of an infection, it's called a fever. Fevers are caused by chemicals called pyrogens flowing in the bloodstream. Pyrogens make their way to the hypothalamus in the brain, which is in charge of regulating body temperature. When pyrogens bind to certain receptors in the hypothalamus, body temperature rises.

One common pyrogen is called Interleukin-1 (IL-1). IL-1 is produced by white blood cells called macrophages when they come into contact with certain bacteria and viruses. IL-1 has multiple purposes, one of which is to signal other white blood cells, called helper T cells, into action.


One purpose of a fever is thought to be to raise the body's temperature high enough to kill off certain bacteria and viruses sensitive to temperature changes. One interesting debate right now, therefore, is, "Should you lower a fever?" Aspirin, for example, will reduce fever; but if the fever is actually helping rid the body of infection, then lowering it might not be a good idea. On the other hand, people sometimes die from fever. Right now the general medical consensus falls on the "reduce the fever" side of the fence.

Temperature virus FAQs

How long does viral fever last?
Fevers can last for as little as 2 to 3 days and for as long as 2 to 3 weeks. The duration of a fever is based on various factors such as the age of the person, the type of virus that infected them, and whether they received prompt treatment.
What temperature kills bacteria?
Bacteria are known to cease functioning and die at temperatures above 165 degrees F. They stop multiplying at temps above 140 degrees. The perfect temperature for bacteria to fester is between 40 and 140 degrees (this is called the "danger zone").
How do you get a viral infection?
The most common way of getting a viral infection is through inhalation. When an infected person sneezes or coughs near you, they release viral droplets that become airborne. These droplets can make their way into your system and cause an infection.
What are 3 common viral infections?
The three most common viral infections are common cold, influenza, and bronchitis. Treatment for these viral infections may require medical attention depending on the patient’s symptoms. In some cases, the body may heal on its own.
Does raising your body temperature help fight viruses?
It has been shown that fevers (which elevate body temperatures) can help the immune system fight viruses. By increasing body temperature, the immune system works more efficiently and makes it harder for viruses to multiply in the body.