Body temperature has long been recognised as a key indicator of health. Far from being a standard quantity, human body temperature is extremely variable and can vary depending on a number of factors.
Doctors have used body temperature as a measure of illness for centuries. For the better part of two centuries, western medicine held normal body temperature or “normothermia” to be 37°C-38°C [98.6 to 100.4 °F]. Since then however, our understanding of normothermia has evolved. We now understand that “body temperature”, far from being consistent throughout, actually refers to a hodgepodge of different temperatures at different locations in the body. For example, if you measure your rectal temperature, you are likely to get a reading that’s higher than an oral measurement. This is because your body is an open system that is constantly interacting with the external environment. At the surface level, the temperature of the body (i.e peripheral temperature) is directly influenced by the ambient temperature. But despite the many factors that influence temperature, your body maintains its core temperature fairly constant.
Core temperature refers to the temperature of the inner organs of the body. The body uses a wide range of mechanisms to ensure that core temperature is maintained within a narrow range that is most suited for the various reactions involved in the body’s metabolic process.
One of the most elementary factors that influence normal body temperature is age. The influence of age on body temperature is most easily observed in the case of children and elderly people. Children tend to have very high metabolic rates, i.e their bodies convert food to energy at a much higher rate, on average, compared to adults. This also translates to kids, on average, having a higher baseline body temperature, than adults.
On the other end of the age spectrum, the opposite is true. Older people, especially those older than 65, generally tend to have lower baseline temperatures than their younger counterparts. And this decline is progressive - this study shows that people in the 65-75 age group had higher peak temperatures than those in the 75-85 and >85 age groups. In addition to having a lower baseline, older people also have more muted immune responses, all of which makes it very challenging to detect infections.
That’s why continuous fever monitoring could be crucial in geriatric care. Because they have lower baseline temperatures, using standard benchmarks to detect fevers are bound to fail. So, it is all the more important that a unique, individualised baseline is established, against which spikes can be caught more readily
It was all the way back in 1868 that the idea of body temperature varying by gender was floated by German physician Carl Wunderlich. Wunderlich claimed that women, on average, tended to have higher body temperatures than men. Numerous theories have been floated to explain this - women having a higher percentage of body fat than men, female sex hormones etc.
A 1993 study found no significant differences in body temperature between its male and female subjects. In fact, this review published in 2019, found that its female subjects, on average, tended to have a slightly lower body temperature than men. However, it dismisses this difference as insignificant.
It has to be noted however, that a woman’s body temperature is higher during ovulation and pregnancy, and lower at the start of the menstrual cycle.
Body temperature undergoes significant fluctuation over the course of a day. This is called “diurnal variation”. It is usually at its lowest early in the morning and slowly climbs up after a person wakes up, reaching its peak late in the afternoon.
This variation corresponds to the level of metabolic activity, which is lowest during sleep and slowly climbs up as the day progresses.
Your muscles need energy to function. During strenuous physical activity, your muscles generate a tremendous amount of heat, which results in an increase in your body temperature. The body tries to dissipate the excess heat in order to restore the body to a normothermic state. However, sometimes, the body finds itself unable to cope with the increase in temperature and lose enough heat to maintain the core temperature stable.
The more work your muscles are required to do, the more heat they generate. The extent to which your body temperature climbs during exercise is linked both to the intensity of the activity and the amount of heat lost by your body. Training in hot/humid conditions makes it harder for the body to keep its core temperature within the normal range. This paves the way for dehydration and/or heat illness, which is extremely dangerous. This is why experts warn against intense exercise in hot weather. The more your body is conditioned to a certain level of physical activity, the better it is at being able to dissipate heat. So, the key takeaways from this should be to be patient and take your time with conditioning your body and to hydrate adequately before intense workouts.
A Continuous temperature monitoring device could offer you insights into how your body is coping with your workout intensity. It uses continuous temperature measurements to assess how your body temperature varies in relation to its baseline. Using continuous temperature monitoring could help you efficiently tailor your workouts to your body’s level of conditioning.
Body temperature increases in response to stressful situations. Stress hormones such as cortisol and adrenaline mediate this increase in body temperature. This increase in temperature is an adaptive response of the body to deal with perceived threats. Adrenaline, which mediates the body’s “fight or flight” response, stimulates increased heat production in the liver, in addition to driving other adaptive changes. The liver being one of the body’s largest and most metabolically active organs, has a notable impact on body temperature.
Click here to know more about psychogenic fever (fever caused by stress and anxiety).
There is usually a slight increase in body temperature shortly after a meal. If you use a continuous temperature monitoring device, you can notice a small increase in your temperature, 20-30 minutes after eating. This reflects an increase in your metabolic rate, to facilitate digestion.
Many pharmaceutical drugs, including several classes of antibiotics (cephalosporins, penicillins etc), methyldopa, phenytoin, among others, are known to cause an increase in body temperature. Additionally, many commonly used recreational substances such as MDMA and cocaine also cause body temperature to rise.
Smoking cigarettes has also been known to cause spikes in body temperature.
Body temperature readings vary depending on the site of measurement. Here are some basic guidelines to understand how temperature readings may vary across the most common measurement sites. As a rule, an axillary temperature is usually 0.3°C -0.6 °C [0.5°F-1°F] lower than an oral temperature and a rectal reading is 0.3°C-0.6°C [0.5°F -1°F] higher than an orally measured reading.
Invasive methods are required to obtain an exact measurement of the body’s core temperature. In many cases, it doesn’t make sense to opt for invasive methods, despite their reliability and accuracy. Rectal readings have been considered a happy middle ground between accuracy and convenience. but in recent years, rectal measurement of temperature has increasingly gone out of favour because of patient reluctance and concerns that it spreads infections.