Fever is a symptom that has plagued each of us at some time or the other. Often, people try to treat fever at home. A better understanding about fever will no doubt help in managing fever better at home; it will also ensure that a doctor is consulted at the right time.

Man is a warm-blooded animal, that is, body temperature is maintained regardless of the environmental temperature. The normal temperature of the body is maintained at 37°C or 98.6°F by the hypothalamus, a small but important part situated just below the brain. A slight variation of 0.5°C or 0.9°F occurs during the day.

Fever is defined as a before-noon temperature of more than 37.2°C or 98.9°F or an after-noon temperature of more than 37.7°C or 99.9°F. Fever is an elevation in normal body temperature that occurs in connection with a raised hypothalamic set point.

Body temperature is measured using a thermometer. The reading is obtained either by placing a thermometer in the mouth, in the rectum (especially in children), from the ear near the ear drum or in the armpit. Rectal temperatures are usually 0.5°C or 0.7°F higher than oral temperatures. Temperatures taken in the armpit are usually not very reliable.

Very high temperature of more than 41.5°C or 106.7°F is called hyperpyrexia. It occurs due to brain hemorrhage or severe infections.

Some causes of fever are listed below:

Infections: Viral, bacterial, fungal or protozoal infections often cause fever. Some additional features that can help in the diagnosis of fever due to infections are:

Fever of short duration without specific symptoms may be due to influenza

Fever with throat pain and difficulty in swallowing could be due to sore throat infection, diphtheria or infectious mononucleosis (infection by a virus called Epstein-Barr virus)

Fever with cough, chest pain and rusty sputum may be due to pneumonia

Fever with rigors and burning while passing urine indicates a urinary tract infection

An alternate day fever with rigors indicates malarial infection

Fever with swelling of feet with rigors and a raised eosinophil count may indicate filariasis

An increasing fever with pain in abdomen, small red spots on the skin and a slow heart rate could be due to typhoid

Fever with neck stiffness, headache and vomiting may be due to meningeal infection (infection of the covering of the brain)

Fever with cough over a long duration and weight loss may indicate tuberculosis

Fever with rashes may be due to a viral infection

Short-duration fever with progressive weight loss and a high-risk behavior could possibly be due to HIV infection

Drugs and Biological Agents: Drugs like beta-lactam antibiotics, procainamide, isoniazid, alpha-methyldopa, quinidine and diphenylhydantoin are associated with fever. Biological agents like interferons and interleukins used in therapy could also cause fever. Vaccines could also result a temporary rise in temperature. Fever caused by drugs is often associated with a rash.

Tissue injury: Heart attack, burns, trauma and injections into muscles damage tissues and can cause fever.

Cancers: Blood cancers like leukemia and lymphoma, and liver cancer can cause fever. The liver, spleen and lymph nodes may be enlarged and easily felt in these conditions.

Inflammatory diseases: Rheumatoid arthritis, systemic lupus erythematosus and inflammatory bowel disease are some inflammatory diseases that could cause a rise in body temperature.

Hormonal diseases: Thyrotoxicosis (a condition in which the thyroid gland is hyperactive) and pheochromocytoma (a condition in which the adrenal gland is affected) can cause fever.

Metabolic diseases: Gout and increase in blood urea can sometimes raise the body temperature.

Genetic diseases: Familial Mediterranean fever is a genetic disease with fever as one of its symptoms.