see also Fever in Children and Fever in Infants
Running a temperature above normal range of 36-37°C (96.8-98.6°F) is usually a sign that the body is fighting some kind of infection. Particularly serious are Pneumonia (temperature above 40°C [104°F], breathlessness, coughing, rust-coloured sputum), Meningitis (fever, headache, nausea, vomiting, stiff neck, light hurts eyes), and Puerperal Fever (marked fever shortly after childbirth); all three require prompt medical attention, so consult your doctor if there is no improvement in 2 hours.
Fever can also accompany such ailments as acute Pyelonephritis (rapid onset of high fever, pain in small of back), Tuberculosis (slight fever, weight loss, fatigue, dry cough, shortness of breath, chest pain), Brucellosis (flu-like symptoms after drinking unpasteurised milk), and of course various tropical diseases, to be on safe side, consult your doctor if there is no improvement in 12 hours.
Other conditions which cause temperature to rise are acute Bronchitis (wheezing, coughing, yellow-green phlegm), Influenza (headache, general aches and chills, runny nose), Gastroenteritis (headache, diarrhoea, vomiting), pharyngitis and Tonsilitis (sore throat, difficulty swallowing), Cystitis (painful urination, frequent urge to urinate), Measles (rash, runny nose, cough, red eyes), Rubella (red rash, pea-like bumps on back of head), Chicken Pox (rash followed by itchy blisters), and Pelvic Infection (lower abdominal pain, foul-smelling vaginal discharge).
Prolonged exposure to sun, especially if humidity is high, can cause Heat Stroke, sending body temperature rocketing to 40°C (104°F) or more; person looks flushed, has hot, dry shin and a fast, thudding pulse, and may lose consciousness; give First Aid.
Homeopathic remedies for fever appear under appropriate condition.