Are you feeling the cold? Don’t worry, your body has got it covered

THE highest body temperature ever recorded was apparently 46 degrees Celsius. That honour goes to a chap from America named Willie Jones, who survived after suffering severe heat stroke.

The other end of the scale is perhaps even more dramatic. In 1999, a young Swedish medical student fell through ice and was immersed in freezing water for 80 minutes before rescuers could get her out. By that time, she was unconscious and ice cold and her heart had stopped beating. Her body temperature was an almost unbelievable 13 degrees Celsius.

I say unbelievable only because she survived. Incredibly, a team of doctors managed to warm her blood slowly in theatre by diverting it outside her body over a period of a few hours before her heart showed signs of life again.

Anything approaching these extremes of human body temperature are a rarity, largely on account of our normally very strictly controlled core body temperature. Depending on where you look, this generally falls between 36.1 and 37.5 degrees Celsius (97.0 to 99.5 degrees Fahrenheit).

The understanding of our relationship between our temperature and our health is a long held one. Early physicians would have been remiss to overlook the fact that those who felt unwell were experiencing chills or felt warm to the touch.

In fact, Hippocrates himself apparently used the hand to the forehead method of measuring temperature, which continued for hundreds of years before other methods evolved.

Galileo was responsible for one of the early more objective ways of measuring temperature through his use of the thermoscope in the early 1600s.

This contraption relied on the fact that changing temperatures caused gas to expand or contract and broadly it consisted of air trapped in a glass tube, one end of which was submersed in water which could then be warmed or cooled accordingly.

Subsequently a plethora of new devices came into being to measure human temperature, each one resembling our modern day thermometers more and more.

It wasn’t until 1868 that a man called Carl Wunderlich drew together thousands of temperature measurements to declare definitively that we humans have a constant core temperature and that, as everyone probably already knew, it varies during disease.

Historically, we have tended to measure core body temperature (different from the temperature of the skin, thus making the hand on the forehead rather unreliable) via the rectum, under the tongue, under the armpit or, most commonly nowadays, in the ear.

The tympanic thermometer was invented only as recently as 1964. Just lately, having had radar-gun-type devices levelled at our foreheads on a regular basis, we are no doubt inclining towards adding another method to that list.

We know that, despite having a pretty constant core temperature, it does still vary a little bit. This depends upon a number of different factors - the weather, physical activity, whether we’ve eaten recently and even our age (our temperatures tend to drop as we age, hence the reason nursing home radiators tend to be turned to maximum so much of the time).

Certain medical conditions, such as hyperthyroidism or hypothyroidism, can also affect your temperature, causing you to feel either hot all the time or cold all the time respectively.

And, of course, hormone surges famously have the potential to cause hot flushes.

It is amazing really with so much going on in the body at any one time that it is able to maintain such a tight temperature control but this is vital for us to function.

Too warm and the metabolic processes will become overworked and too cold and the metabolism will slow. Either of the above scenarios places risk on the health of our vital organs.

Homeostasis is the term we give to the body’s fine balance of physical and chemical processes. Besides temperature, this includes blood pressure, sugar levels, electrolytes and fluid balance.

Throughout the body, we have thermoreceptors (temperature sensors) that feed back to the area of our brains known as the hypothalamus. If things look like they are tilting one way or another, the hypothalamus is able to feed back in various different ways to readjust the balance. It’s a bit like the plate spinner of the human body.

Humans are endotherms (warm-blooded), so we can generate heat internally by way of our metabolic processes. If we are cold, we increase our metabolism to produce more heat. If that doesn’t work, we might restrict the blood flow to the skin where a lot of heat is lost and start shivering, which creates more heat energy.

Exotherms, such as reptiles, are, a little misleadingly, called cold-blooded because they rely more on external heat sources, which is why you see lizards or snakes basking in the sun.

If we are too warm, we need to get rid of heat. Slowing our metabolic processes is the first step and diverting our blood to the skin is another way. If the surrounding air is warmer than we are, the body starts to sweat and the evaporation of the water from our skin removes heat energy. Furry animals that can’t sweat achieve the same result by panting.

All of this is remarkably effective but when our temperatures go above 38.0 degrees Celsius, this is generally termed a fever.

Usually when this happens we have some sort of infection so the normal processes that would bring the temperature down are bypassed.

Why does the body allow this? Well, although a fever makes us feel pretty unwell, it is a necessary evil in the immune response to an infection. The white cells that represent the body’s defence produce various chemicals upon contact with a pathogen that feed back to the hypothalamus, causing it to set a new higher core temperature target.

It is thought that our immune response is better at these higher temperatures, plus the viruses and bacteria that might be causing an infection are not keen on a warmer environment.

Often during infection, one might feel cold even though there is a fever. Because there is a new target temperature, it may be that the perceived sensation is that of a chill even if the temperature is raised.

If the body really wants to raise the temperature quickly, it may cause your muscles to shake in the same way they do when you are cold. These uncontrollable “rigors” are often a sign of a more severe infection and you should probably contact a doctor if you are experiencing them.

A fever is therefore not necessarily something you need to get rid of at all costs. In children, as long as a child is not in discomfort and feeling unwell, you do not need to give medication such as ibuprofen or paracetamol just because there is a fever.

Although higher temperatures tend to signify more severe infections, a judgement should be made more on how they are in themselves rather than the temperature alone.

It is also not a great idea to remove a child or baby’s clothes should they spike a fever, nor is it a good idea to place a flannel over one’s forehead, regardless of age, as this will confuse the body’s innate thermoregulators.

And it should be said that these thermoregulators tend to do a pretty good job in general if left to their own devices.

So, as the nights draw in and it gets a bit colder, I suspect we’re all beginning to wrap up warm.

However cold you feel, it may be reassuring to know that, even though your fingers are chilly and your nose feels a bit numb, your brain, your heart, your liver — all the stuff that counts — will be none the wiser.