While 19th-century German physician Carl Wunderlich recognized 98.6 degrees Fahrenheit as the normal human body temperature, most healthy temperatures range from 97 to 99 degrees Fahrenheit, according to Boots and WebMD. Temperature usually varies by age, activity level and the time of day.
An oral temperature surpassing 100.4 degrees Fahrenheit in adults indicates a fever. Fever causes include infection, heat exhaustion and medications such as narcotics, barbiturates, antihistamines and antibiotics, notes WebMD. An abnormally low body temperature can result from cold exposure, alcohol consumption and hypothyroidism. It can also result from infection, particularly sepsis. A body temperature below 95 degrees Fahrenheit classifies as hypothermia, notes Healthline.