Time of day
When we are asleep we have decreased heat production, metabolism and activity. It is not uncommon to observe sweat in sleeping persons, especially children, at a lower temperature than usual. Body temperature is usually lowest between the hours of 2:00 and 06:00.
During the day, the temperature rises between 0.5 and 1°. By measuring temperature in the morning and in the afternoon, one expects a higher temperature in the afternoon.
Children, newborns and premature babies have little ability to react to temperature fluctuations, and thus have little ability to keep the body temperature stable. The temperature in children can be up to 1° C higher than normal.
Older people’s ability to maintain stable and normal body temperature is reduced due to decreased temperature sensation. Heat loss is greater when the amount of subcutaneous fat is reduced in addition to reduced elasticity of blood vessels and decreased ability to sweat. Older people can be unwell without a pyrexia and can quickly develop hypothermia as previously discussed.
Adult temperature often rises during heavy muscle activity. Generally we adjust to temperature fluctuations by adjusting our environment e.g. clothing, room temperature.
Increased production of thyroxine increases metabolism and thus body temperature. Decreased production of thyroxine has the opposite effect. Epinephrine can increase the temperature. Fertile women often have a higher temperature of about 0.5° C two days before ovulation.
This phenomenon is used diagnostically with women who have fertility problems. Women are asked to take the temperature for a few months to see if they have high temperature to assess when they are ovulating.
Nutritional intake can cause temperature rise by 0.1 to 0.3° C. The rise in temperature occursis approximately 20 to 30 minutes after a meal. People who are malnourished are more susceptible to hypothermia due to reduced body fat. Dehydration can also increase body temperature.
Powerful muscle activity can increase the temperature considerably. This stabilizes after about half an hour.
In hot environments body temperature can increase without meaning that a person is unwell as it is the body’s natural adjustment to the environment. However if you stay in cold areas the body temperature normally does not change except in children and older people , who may experience a drop in the body temperature rapidly so need to be observed closely.
Bacteria, viruses, toxins, and chemical reactions of the body’s inflammatory response may cause pyrexia. Tissue damage following a myocardial infarction is usually associated with pyrexia.
A pyrexia immediately after surgery is normal. Generally it stabilizes within three to four days. However a persistent pyrexia or sudden rise in temperature, three to four days after surgery can indicate an infection.
Medicines can affect the circulation or metabolism and thus affect body temperature.