What causes a fever?

Although you feel lousy when you have a fever, a fever actually is good for you. Your increased body temperature stimulates white blood cells to produce antibodies, which fight off an infection. Some bacteria and viruses only can survive in a narrow temperature range, so heat can inhibit their production or kill them. A fever starts because the body's immune system identifies microbes from a bacteria or virus. The immune system then releases chemicals called cytokines into the bloodstream, which stimulate the body's thermostat, called the hypothalamus, in the brain. The hypothalamus raises the body's temperature by constricting blood vessels in the skin and causing skeletal muscles to contract, which makes us shiver.

A fever is a temporary increase in the body's temperature in response to some disease or illness. Some of the possible causes of a fever include:

• Viruses
• Bacterial infection
• Heat exhaustion
• Some malignant tumors
• Blood clots or thrombophlebitis
• Appendicitis
• Tuberculosis
• Skin infections or cellulitis
• Some immunizations, such as the diphtheria, tetanus and acellular pertussis (DTaP) or pneumococcal vaccines
• Exposure to extremely high temperatures

A fever is usually a sign of an underlying medical condition. Below are some of the most common causes of fevers:

• Infection: Most fevers are symptoms of an underlying viral or bacterial infection in the body. However, any type of infection, including fungal and parasitic infections, may cause fevers. As the immune cells in the body fight off an infection, they generate heat, which leads to an increase in body temperature. Normally, part of the brain, called the hypothalamus, regulates the body's temperature. However, when an infection is present, substances called pyrogens prevent the brain from properly controlling the body's temperature. This is actually considered a positive response because the viruses that cause colds and other infections thrive in cool temperatures.
• Extreme sunburn: Severe sunburn may cause a fever and chills.
• Exposure to hot environments: Some people may develop a fever when the body becomes overheated. This condition, called hyperthermia, often occurs as a result of vigorous exercise or after exposure to extremely hot or humid weather. Hyperthermia is treated differently than other causes of fever. The affected person must be cooled immediately. The advanced stages of hyperthermia are commonly called heatstroke or sunstroke.
• Medications: A fever may be a side effect of certain medications, such as antibiotics, blood pressure-lowering drugs, antidepressants, antihistamines, and drugs used to treat seizures. Some infants and young children develop fevers after receiving routine immunizations, such as the diphtheria, tetanus, and acellular pertussis (DTaP) vaccine.
• Unknown origin: In some cases, there is no known cause of a fever. If a person has a body temperature higher than 100.9 degrees Fahrenheit with no known cause, a doctor may diagnose the condition as "fever of unknown origin." In such cases, treatment focuses on reducing the fever, rather than the underlying cause.

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• cold
• mumps
• sore throat
• measles
• earache
• pneumonia
• diarrhea
• bronchitis
• urinary infection
• appendicitis
• roseola
• meningitis
• chickenpox
• female reproductive infection