Normal human body temperature, also known as normothermia or euthermia, is a concept that depends upon the place in the body at which the measurement is made, and the time of day and level of activity of the body. The normal temperature of the human body is around 99°F (37°C) though this fluctuates quite normally from slightly lower in the morning to higher in the evening. The core body temperature of an individual tends to have the lowest value in the second half of the sleep cycle; this low point, called nadir, is one of the primary markers for circadian rhythms. This level is controlled by a centre in the brain, which co-ordinates the various ways in which the body can regulate its own heat, such as sweating to lower temperature, or shivering to produce some heat from the muscles.

Temperature is increased after eating, and psychological factors also influence body temperature. Many outside factors affect the measured temperature as well. "Normal" values are generally given for an otherwise healthy, non-fasting adult, dressed comfortably, indoors, in a room that is kept at a normal room temperature (22.7 to 24.4 °C or 73 to 76 °F), during the morning, but not shortly after arising from sleep. Furthermore, for oral temperatures, the subject must not have eaten, drunk, or smoked anything in at least the previous fifteen to twenty minutes, as the temperature of the food, drink, or smoke can dramatically affect the reading. Children develop higher temperatures with activities like playing, but this is not fever because their set-point is normal. Elderly people may have a decreased ability to generate body heat during a fever, so even a low-grade fever can have serious underlying causes in geriatrics. Normal body temperature may differ as much as 1.0 °F between individuals or from day to day.

The temperature reading taken by your doctor depends on which part of the body is being measured. Measurements are commonly taken in the mouth, the ear, the anus, or the armpit. In females, the vagina is sometimes also used. The median daytime temperature among healthy adults are as follows:

• Temperature in the anus (rectum/rectal), vagina, or in the ear (otic) is about 37.6 °C (99.6 °F)
• Temperature in the mouth (oral) is about 36.8 °C (98.2 °F)
• Temperature under the arm (axillary) is about 36.4 °C (97.6 °F)

Normal human body temperature varies slightly from person to person and as mentioned above by the time of day. Consequently, each type of measurement has a range of normal temperatures. The range for normal human body temperatures, taken orally, is 36.8±0.7 °C (98.2±1.3 °F).This means that any oral temperature between 36.1 and 37.5 °C (96.9 and 99.5 °F) is likely to be normal.

A number of essential oils have the effect of helping to raise, lower or normalise the body temperature. Bergamot, Eucalyptus, Lavender, Melissa and Peppermint oils will all help to reduce body temperature, and oils which promote sweating, such as Cypress and Rosemary will do so indirectly. They can be used in baths, or mixed with plenty of cool water and sponged over the body.

Brisk massage, even without the addition of essential oils will help to raise body temperature quite effectively, but if you add a warming oil such as Marjoram or Thyme it will be even better. Any of the oils described as rubefacient will increase the local circulation and help to induce a feeling of warmth, especially in cold extremities. These include Black Pepper, Juniper and Rosemary.

The temperature control mechanism is less efficient in babies and elderly people, so variations in their temperature need to be watched carefully.

See also FEVER.