Humans are endothermic. This means our bodies produce their own heat, constantly regulating the core temperature to keep things in balance. The body does this unconsciously and automatically, but sometimes it fails. When the balance is broken, the body can become too hot or too cold – either of which usually indicating the onset of illness.

This article will look at what the average body temperature is, how it varies across different people, and the signs of body temperature changes, such as fever.

The average human body temperature

Your core body temperature varies depending on several factors. Most sources will tell you that that the human body should have a core temperature of around 37⁰C *. While this is indeed the case, it’s worth recognising that it is an average and each person’s body operates slightly differently. In fact, the actual numbers may depend on how old you are and various other factors, such as the time of day, physical movement, and sustenance. So if your temperature varies by a degree or so from this average it is not necessarily a cause for concern. It’s also worth noting what the averages are for different people in your family:

Babies & children:

A newborn baby (0-3 months) will have a temperature reading of between 36 – 37.6⁰C when taken in the ear which is lower than the adult average**. This is also similar for prepubescent children.

Elderly:

In older people(65 years and over), body temperature drops slightly from the adult average of around 37⁰C to 35.8⁰C *.

Pregnancy and menstruation:

When pregnant, women can have a slightly higher than average. Temperature may also go up or down depending on a woman’s menstrual cycle, so keep this in mind if you’re ever taking a reading***.

Other factors:

Slight variances are common, as many harmless conditions can raise or lower body temperature. Exercise will raise it, for example, as will consuming hot food and drink. The time of day may also cause slight differences as the body grows more active towards the afternoon and starts to warm up.

When the human body overheats

On its own, having a slightly higher or lower body temperature is not something to worry about. If someone has a viral infection, the body will often raise its core temperature to help fight it off. With a little rest, and plenty of food and drink, they’ll soon recover/

One thing to be wary of is dehydration. This is caused by excessive sweating as the body tries to regulate its temperature, so make sure someone showing signs of fever drinks plenty of fluids.

There is a point where high temperatures do become a cause for concern. When dealing with children over 36 months through to adults, any temperature reading over 37.7⁰C indicates a fever. And if this rises above 39.4⁰C, you should call emergency healthcare services or your local GP. Anything over 40⁰C, and the body becomes so hot that organs can begin to fail****.

In infants aged 3-36 months, the fever is indicated at 37.6⁰C, and a high fever is defined as anything over 38.5⁰C. In babies aged 0-3 months fever is diagnosed if their temperature rises to 37.4⁰C or above. Increased temperatures can be especially serious in young children and infants, as it may indicate a bacterial or viral infection. If young children or babies develop a fever, call a doctor.

Diagnosing a fever

As stated before, a slightly higher than normal temperature in isolation does not necessarily indicate a fever. Lots of factors are behind that, and in most cases, it will pass without too much discomfort. You should only start to suspect a fever if a high temperature is accompanied by the following symptoms:

  • Loss of appetite
  • Sensations of coldness or chills, accompanied by shivering
  • Aching muscles
  • Cold sweat
  • Headaches

Fevers are not an illness in themselves. Usually, they are the body’s reaction to fighting off a viral or bacterial infection. Most fevers can be treated at home: drink plenty of fluids, get plenty of rest, and keep yourself at a comfortable temperature.

You should only call a doctor if your temperature exceeds the danger point, or if the fever is joined by a stiff neck, an unusual rash, or difficulty with breathing. It’s also important to realise that a fever isn’t the only indicator of illness. In fact, someone could be ill with no signs of fever at all – so check for other symptoms and consult a doctor when in doubt.

*Hutchison, James S.; et al. (June 2008). "Hypothermia therapy after traumatic brain injury in children". New England Journal of Medicine. 358 (23): 2447–2456. doi:10.1056/NEJMoa0706930. PMID 18525042. And Pryor, Jennifer A.; Prasad, Ammani S. (2008). Physiotherapy for Respiratory and Cardiac Problems: Adults and Paediatrics. Elsevier Health Sciences. p. 8. ISBN 0702039748.
**Source: D002519-CR-THR11-01-IRT6030.6520_rev 5
***Baker, Fiona C.; Waner, Jonathan I.; Vieira, Elizabeth F.; Taylor, Sheila R.; Driver, Helen S.; Mitchell, Duncan (2001-02-01). "Sleep and 24 hour body temperatures: a comparison in young men, naturally cycling women and women taking hormonal contraceptives". The Journal of Physiology. 530 (3): 565–574. doi:10.1111/j.1469-7793.2001.0565k.x
****McGugan EA (March 2001). "Hyperpyrexia in the emergency department". Emergency Medicine. 13 (1): 116–20. doi:10.1046/j.1442-2026.2001.00189.x. PMID 11476402.