Typical body temperature is a balance of heat production and heat loss. An area in the brain called the hypothalamus (hi-poe-THAL-uh-muhs) — also known as your body's "thermostat" — monitors this balance. Even when you're healthy, your body temperature varies slightly throughout the day. It can be lower in the morning and higher in the late afternoon and evening.

When your immune system responds to disease, the hypothalamus can set your body temperature higher. This prompts complex processes that produce more heat and restrict heat loss. The shivering you might experience is one way the body produces heat. When you wrap up in a blanket because you feel chilled, you are helping your body retain heat.

Fevers below 104 F (40 C) associated with common viral infections, such as the flu, may help the immune system fight disease and are generally not harmful.

Fever or elevated body temperature might be caused by:

A viral infection
A bacterial infection
Heat exhaustion
Certain inflammatory conditions such as rheumatoid arthritis — inflammation of the lining of your joints (synovium)
A cancerous (malignant) tumor
Some medications, such as antibiotics and drugs used to treat high blood pressure or seizures
Some immunizations, such as the diphtheria, tetanus and acellular pertussis (DTaP), pneumococcal or COVID vaccine

Fever

Overview

Symptoms

When to see a doctor

Causes

Complications

Prevention