Decoding the puzzle of fever – how it evolved and what it does to help fight off infections

When you’re sick with a fever, your doctor will likely tell you it’s a sign that your immune system is defending you against an infection. Fever typically results from immune cells at infected sites sending chemical signals to the brain to raise the set point of your body’s thermostat. So, you feel chills when the fever starts and feel hot when the fever breaks.

However, if you were to ask your doctor exactly how fever protects you, don’t expect a completely satisfactory answer.

Despite scientific consensus that fever is beneficial in fighting infections, exactly how is contentious. We are a veterinary pathologist and an emergency physician interested in applying evolutionary principles to medical problems. The evolution of fever is a classic conundrum because fever’s effects seem so harmful. Besides making you feel uncomfortable, you may also worry you’ll dangerously overheat. It is also metabolically costly to generate that much heat.

In our research and review, we propose that since fever occurs throughout much of the animal kingdom, this costly response must have benefits or it never would have evolved or been retained across species over time. We highlight several important but rarely considered points that help explain how the heat of fever helps your body fight infections.

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