BBC HomeExplore the BBC
This page has been archived and is no longer updated. Find out more about page archiving.

Accessibility help
Text only
BBC Homepage
BBC Radio
BBC Radio 4 - 92 to 94 FM and 198 Long WaveListen to Digital Radio, Digital TV and OnlineListen on Digital Radio, Digital TV and Online

Radio 4 Tickets
Radio 4 Help

Contact Us

Like this page?
Send it to a friend!


Go to the Listen Again page
Tuesday 14 February 2006, 9.00-9.30pm
 Print this page
Back to main page




Programme 6. - Body Temperature


TUESDAY 14/02/06 2100-2130













This is Morland House Surgery in Wheatley in Oxfordshire. We have 10,000 patients in this practice, about 500 children under the age of five and in any one morning we'd expect to see one or two children with a fever.

GP Anthony Harnden in the waiting room of his busy surgery in Oxfordshire, where I will be returning later in the programme to discover the latest thinking on high temperatures in children. It's now second nature to reach for paracetamol or ibuprofen when a child develops a fever but is that always the right thing to do?

At the other extreme - of both age and temperature - I'll be finding out why the elderly are so sensitive to the cold , and what to do with a friend, neighbour or relative you suspect may have hypothermia.

And, sandwiched between the two, a report from the Royal Free Hospital on Raynaud's disease - a common cause of cold, painful hands and feet that's often triggered by a drop in temperature.

When I'm indoors I have to make sure that I've got lots of warm clothes, lots of layers on, boots, sheepskin gloves, scarf and hat - most important.

Thirty seven degrees Celsius - or 98.4 degrees Fahrenheit - is the average normal body temperature, as measured using a thermometer under the tongue. If you use a rectal thermometer, or one of the modern types that go in the ear, then add half a degree, making normal 37.5, because they reflect the core temperature of the body better than the slightly cooler mouth.

But why is it so crucial to maintain body temperature between such tight parameters - and what happens when we don't? My guest today is Professor Bill Keating from University College London.

Bill, what's so special about 37 degrees Centigrade?

Well there's nothing special about it, except that it's pretty near the upper range of temperatures that you get in the world and as it's a lot easier to lose - control your loss of heat than to keep cool in the presence of a hotter environment, it's convenient to have your body temperature at near the upper end of the range of earthly temperatures.

And presumably all the systems within our body are optimised at 37 degrees Centigrade?

That's right. Once you can stabilise your body temperature to a particular level everything else in the body can be adjusted so that it works best at that temperature.

How do we maintain it at such a constant level?

Well in order to prevent yourself from cooling, which is what we're doing most of the time, you can shut down blood flow to the skin. And how effective that is, of course what it does is to turn the skin and the fat under it into basically a layer of insulation inside you, it's like having a layer of clothes inside you. And so once you do that you cut out a loss of heat but of course it depends very much on how thick the fat is. So fat people are much better off than thin people, particularly in water where you've got no external insulation.

I think most people get to the concept that we can get ourselves warm because I mean we are burning energy the whole time, we've got responses for keeping ourselves warm, but the thing I find very difficult to get my head round is how do we keep cool in temperatures above 37 degrees, so say I go on holiday to Oman or somewhere very hot like that, where it can be 45 quite easily, how on earth can we maintain a body temperature of 37 when the outside environment is warmer than we are?

Well it's - it is at first sight a real problem because if you react the way we do to keep cool when the temperature is below body temperature we put a lot more blood to the skin and as long as the outside temperature is lower that helps get rid of heat. But of course as you said the trouble is if the outside temperature is even hotter all that does is to take in more heat from the environment. The only solution then is sweating because once you sweat you can then evaporate the sweat and the evaporation cools the skin down, it's latent heat - technically latent heat of evaporation. And so you can keep cool in a hot environment provided you can sweat, provided the air isn't saturated so that you can evaporate the sweat. And in Saudi Arabia during the Haj where they had a lot of problem with heat stress in people, when the Haj comes into the hot time of year, the standard way that they developed for using this was a British device for putting a spray of water over people and a powerful fan and even in the desert at 45 degrees Centigrade that'll cool them down by evaporation, even though the temperature's higher outside.

Why do we develop high temperatures when we become ill?

Well this is an interesting one, the answer isn't completely known but one of the main theories is that the - most of the bacteria that infect us do better at temperatures rather below body temperature. So that if you put the body temperature up you boost the body's ability to defend itself, the defence mechanisms of the body, but you harm the bacteria's and virus's ability to do them damage.

So a fever's a defensive response to infection, in which case are we treat it as a troublesome symptom that's best alleviated by a couple of paracetamol? A question I put to GP Anthony Harnden, who's involved in research at the University of Oxford into the role of high temperatures in children.

But first, how reliable a sign of serious illness is fever?

One of the studies that we did was looking at children who actually had severe meningococcal disease, some of which had meningitis, some of which had septicaemia. And it was interesting actually that a lot of these children actually had lower temperatures rather than higher temperatures and it might ...

What lower than normal or fevers but not very big ones?

Fevers lower than you would expect. And so they actually had rapid pulses for a fever of about 37-37½, so almost not a fever. And it might be that earlier warning signs are actually a lower temperature for a given pulse measurement, which is why in Oxford that we're conducting a large prospective study to look at all temperature and pulse measurements in children presenting to primary care with a view to actually giving doctors a table of sort of normal values for pulse for temperature measurement so that if a child either fitted - came outside that normal range then the doctor might be thinking that there may be something a little bit more serious going on than the self-limiting infection.


So they'd look at the two parameters and it's their relationship that's important, rather than ...

Yes, than the absolute level of temperature or absolute level of pulse, yes.

In modern medicine one of the key things we do, particularly in children, is we specifically go out to cool them down, we use antipyretic drugs, fever lowering drugs, like paracetamol and ibuprofen and we give advice about stripping children off etc., are we actually then potentially prolonging their infection?

Well it's a very interesting point Mark and I think that's almost certainly true because there have been a number of very interesting studies in this area looking at response to antipyretic drugs, drugs that lower temperature, and if you look at children with malaria, for instance, there was a big study in the Gambia showing that all children receive treatment for malaria but some received drugs to lower their temperature and those that received the drugs to lower their temperature actually had a longer time to clear their parasites by about 16 hours. The same is true for chicken pox, that lesions take longer to cure for chicken pox. And the same is actually true for adults that are experimentally infected with the cold virus - they probably shed more virus if they're treated with temperature lowering drugs for longer periods, i.e. are more infectious than if they weren't treated with those drugs. So although we all get very anxious about fever and I'm a parent myself and I know how anxious temperatures in children can be, it probably is best actually to maintain the child's temperature at a higher level, unless it gets to such a level that the child becomes uncomfortable and irritable and that's when we feel that we ought to be treating them. But fever itself isn't dangerous, unless it gets to a very, very high level, which is rare.

When I was training I worked as a paediatrician in a hospital for a while and one of the things we were always worried about was febrile convulsions, seizures that occur in children with high temperatures, normally in children under the age of five. They're now actually quite common, they affect something like 1 in 30 children so that potentially is a risky side of leaving a high fever.

I think - I think that's right but the children that actually get febrile convulsions are children that actually have a rapid rise in temperature, very rapid rise, and often even if they're given antipyretics they might convulse anyway. So I don't think that the evidence is very strong that actually treating children with temperature lowering drugs actually prevents febrile convulsions, though of course if you have a child that has a febrile convulsion it's extremely worrying and extremely alarming and it is standard advice now to give those parents advice to bring the temperature down if a child has already had a febrile convulsion. But I'm not quite sure that there is great evidence that it actually prevents them.

Well if there is a lack of evidence there and there's also evidence to suggest that fever may be useful in eliminating infection why is it such widespread practice to actively lower temperatures?

One of the reasons is that doctors are presented often in surgery with lots of children with minor self-limiting illnesses and the doctor feels that they ought to do something and it's almost an excuse for not having to prescribe an antibiotic, which is what parents want. So it might actually reduce antibiotic prescriptions by giving advice to lower temperature. The other thing of course to remember is that temperature can make children feel very uncomfortable and we are in the business of alleviating symptoms, as well as trying to cure all illnesses and actually giving children paracetamol when they're feeling uncomfortable and irritable and got a high temperature can actually make them feel a little bit better.

Dr Anthony Harnden talking to me in his surgery in Oxford.

I feel duty bound to point out that it is still standard practice to take steps to reduce a high fever in children under five to try and reduce the likelihood of febrile convulsion and that most doctors and their patients value the symptomatic relief gained from drugs like paracetamol. And if that means prolonging the illness slightly then it may be a price worth paying.

You're listening to Case Notes, I'm Dr Mark Porter and I am discussing body temperature with my guest Professor Bill Keating.

Bill, one thing that's always mystified me when people have a high temperature is why they shiver and feel cold.

Ah that's what causes the high temperature, rather than being caused by it. Because what really triggers the fever off is that the bacteria produce stuff called endogenous pyrogen, which gets to the brain and makes you - makes it react as though the body's too cold. And when you're too cold you [indistinct word] constrict, you shut down the blood vessels in the skin to conserve heat and you also shiver because that produces a lot of heat, it'll produce 10 times your resting heat production. Now that's what shoves the fever up.

So it's actually fooling you into thinking that you're cold so you take the compensatory mechanisms and actually push the temperature up.

That's it.

What happens if the temperature goes too high, is there a magic figure above which it becomes catastrophic?

Yes there is. At around 43-44 degrees Centigrade you start to cook your body tissues and that's fatal. Being too cold you can recover from but if you get too hot, once you've cooked the body tissues, denatured the protein, there's no recovery, they're dead.

So this denaturing is the irreversible change - I suppose the most common denaturing people see is when they cook an egg white - it goes from being clear to white - it can never go back to being clear again.

That's exactly the same thing, yeah.

What about the effect of high external temperatures, we heard about the French heat wave where people were dying, what happens there?

Well when it's fairly minor, the kind of thing we get in this country on a really hot day, you do get people dying as a result of it but that's really because they get dehydrated. And the blood gets more concentrated, it's more liable to clot and so your statistical chance of having a heart attack or a stroke is increased with the blood clotting in the arteries, lining the heart and the brain. So that's really a sort of a statistical thing, you've just got a bigger chance of falling foul of one of these things. But if the - if the temperature goes up a lot more than that you really - you are in dead trouble from denaturation. And then the French heat wave this was really happening, people were dying of simple overheating. It was partly that they had no experience, people in Southern France were getting hotter temperatures but they didn't have anything like this mortality but in Central France they had never experienced this before, people did not know what to do and they basically just didn't do the things that you should do if you need to cool down in these conditions.

Of course excessive heat is only one extreme - excessive cold is a much more common problem here in the UK. Not that temperatures need to plummet that low to cause problems. Indeed for the millions of people with Raynaud's disease, just a slight drop in temperature - the type they may experience when leaving a warm house to go outside, or putting their hands under the cold tap at the kitchen sink - can be enough to give them trouble.

Raynaud's is caused by spasm of the arteries supplying the extremities. The classic tell-tale signs are fingers and hands that turn ghostly white when exposed to cold - and turn red or purple when they warm up again and the blood flow starts to return.

We sent Claudia Hammond to the Royal Free Hospital in London to find out more.

Morning Patricia, so how is your Raynaud's at the moment? Have you had ulcers on your fingertips during the winter over the last few years?

Yes I have. One in particular - this finger - on the right hand...

For Patricia her Raynaud's all started 30 years ago, when she noticed how numb her fingers were.

I used to knit a lot at that time, it was just one finger just appeared white and I thought I was holding the wool too tight round the finger. Carried on for a year or so and I went to the GP and he just said oh I think that's Raynaud's. I've had numerous ulcers on the fingers and I've had a lot of them lanced as well which is not very pleasant. But that is better because it stops the throbbing.

So Dr Chris Denton you are Patricia's doctor and looking after her here at the Royal Free Hospital, but you're a rheumatologist, why does Raynaud's come under rheumatology?

Well Raynaud's is a very common condition but in some cases it's a warning sign or an early feature of a rheumatic disease or a connective tissue disease such as lupus or scleroderma and these are very rheumatological diseases that we care for and that's why Raynaud's really has become an area of expertise for us.

It was really bad, I mean very painful in the winter especially. But even in the summer you can have attacks. I've been in places like Cyprus where it's been 90 degrees and all of a sudden my hands have turned black. But it's just doing the simple things in life like fastening a button, you drop a coin on the floor, there's no way you can pick that up and sometimes you get embarrassed and sometimes people don't want to touch your hands as well - shop assistants, you pass money across and they see your hands and they just jump back, that's quite embarrassing as well.

Primary Raynaud's is very common and almost a variation of our normal tendency to lose blood flow when we get cold and that can affect up to about 1 in 10 people and particularly young women are affected.

Now lots of people will be used to having very cold hands and hands and feet that sort of seem not to get warm and I certainly have that myself. But this is much more serious than that isn't it.

Yes it is, particularly when it's associated with an underlying connective tissue disease you get blood vessel damage, as well as a spasm of the blood vessels and then you can start to develop problems with ulceration over the fingertips and changes in the skin over the fingertips and a lot of pain and loss of sensation in the fingers as they're deprived of blood supply.

I was reading that one of the ways of testing whether people have Raynaud's or not is that sometimes you get people to stick their fingers into a bucket of iced water and then look to see what happens. Do you really do that?

Yes, we do perform what's called a thermal challenge to confirm or assess the severity of Raynaud's but we don't put patients' hands in iced water, it's water that's at 16 degrees, so it's just cool water, and then we can assess the time taken for the blood flow to return to the fingers using a thermal image.

I'm in - I mean at the moment I am a little bit cold but probably in two minutes time they might warm up, they might go red.

Many patients find that adjustments in lifestyle do make a difference, avoiding precipitating factors, making sure that you're wearing the right clothing, trying to avoid getting a low body temperature in general. Medical treatments can be useful and there are prescription drugs that are given to try and reduce blood vessel spasm.

So would the drugs that the patients are given be the same sorts of drugs that are given to people for high blood pressure?

In general many of the treatments for Raynaud's have come from other branches of medicine, particularly cardiology and hypertension. And so drugs that open up blood vessels, vasodilators, are useful to treat high blood pressure and also can be useful to prevent Raynaud's attacks.

And I was reading that there'd even been trials in Germany of using Viagra.

Viagra or sildenafil has been used to treat Raynaud's, particularly severe Raynaud's. It's perhaps not surprising that a drug that is known to help the blood vessels in the lung is also helping the blood vessels in the extremities and there have even been trials of fluoxetine or prozac, which is an antidepressant drug, which seems to have independent of its effect on mood a beneficial effect in some patients on Raynaud's phenomenon. It seems to work by reducing some of the chemicals in the blood which trigger blood vessel spasm.

Dr Chris Denton ending that report from Claudia Hammond.

Raynaud's disease can be very debilitating but it shouldn't be life threatening - unlike hypothermia, another, fortunately less common complication of living in a country with cold winters.

Bill, at what sort of body temperature do we start using the term hypothermia as opposed to just feeling cold?

Well there's a sort of rather arbitrary level at 35 degrees Centigrade which has been set, when you're below that you're said to be hypothermic.

So that's a couple of degrees below normal body temperature. It's mainly a problem in the elderly, particularly at this time of year, is it because they're less tolerant of the cold?

Well it's mainly probably because most of them or many of them are rather thin, you do get some elderly people who become very thin either because of illness or for other reasons but whatever it is if you don't have any fat under the skin you don't have any insulation, we don't have much insulation when you [indistinct word] and shut down the blood vessels to your skin. So you're much more prone to lose heat. And also they tend to be able to shiver rather less readily than younger people and they have other - other sorts of problems too - they don't react so quickly to heat and cold, they do initially but if the temperature keeps swinging about they get tired of reacting to it and the responses decline.

But how do you tell if someone has hypothermia? Well Rebecca Neno is a nurse and leader of the Caring for Older People Programme at Thames Valley University.

In the very early stages the person would be shivering, they would be looking for more clothes to put on and trying to get warm. However, as the hypothermia continues this shivering ability will decrease and then it becomes quite difficult to identify.

How should we deal with someone who's got hypothermia?

Even if the patient is suffering from what we'd know as shock we shouldn't be raising the patient's feet, for example, we shouldn't be rubbing their extremities to try and get them warm, which is often a common thing that people would engage in. And that's because as the body cools down with hypothermia the extremities are shut off, if you like, the blood flow to the extremities decreases to ensure that the main organs are diffused with blood and the core body temperature maintained. Therefore if we start rubbing the extremities or raising the feet that cold blood that is sitting at the extremities would move to the core of the body and could in fact worsen the hypothermia. So that's an important point.

What about warming somebody up too quickly, I mean you find your grandmother, for instance, and she's freezing cold, a little bit confused and the simplest way might be to pop her into a warm bath - why shouldn't you do that?

I mean really exactly the same reasons as I've just said - if you're warming people up too quickly the cold blood sitting at the extremities can move into the core and lower that core body temperature, obviously making the condition worse.

So once the patient's in hospital is there any other specialist techniques that are used to accelerate warming?

Yeah there are. Obviously hospital staff have access to special warming blankets; administration of intravenous fluids through a drip, which are warmed; inhalation of warm humidified gases for example - and obviously that's very specialist treatment which would be done within - immediately within an A&E department and the patient transferred on to further settings depending on the severity of the hypothermia.

But while hypothermia may be life threatening most of the risk associated with getting too cold is the effect that a drop in temperature has on other conditions - particularly chest problems, stroke and heart attack. Dr Paul Wilkinson is an environmental epidemiologist at the London School of Hygiene.

People die of hypothermia but it's not a very common condition I think. A lot of people die of cold related problems - cold related illnesses - but the increase in the frequency of deaths and cases of illnesses are really in the common diseases. So the big increases which occur in winter are things like heart attacks, strokes, respiratory illnesses. And we do see a big excess of those over the winter months by comparison with the death rates you'd expect during summer, there is maybe 21 or 2% increase. And depending on how you count them you can estimate the winter excess of deaths nationally be somewhere between about 30 and 50,000 each year. And if you look at the pattern of deaths across a year and in relation to outdoor temperature you will see that there is a steady rise in almost every population you look at once the temperature goes below a certain level. In the UK that level is actually quite high, it's sort of the high teens, maybe 17 or 18 degrees Celsius as the maximum daily temperature, of course that means the average and the night time temperature's much lower but any temperature below that you start to see a gradual increase in death rates. And the rule of thumb is roughly for each degree Centigrade of cooling, below that threshold you get about 2% increase in death rate.

I think there is more than one possible mechanism but I think that the main one that I believe is likely to give rise to the excess of deaths is the one that is related to clotting of the blood and the circulation. As you chill, as you get colder, a number of things happen to the circulation and also to the blood itself. Essentially one of the key things is that you constrict your blood vessels, particularly in the periphery, so in your arms and legs, they squeeze and actually what that does is squeeze fluid out of the circulation, but it concentrates some of the proteins and other parts of the blood left behind and that includes those elements of blood which contribute to blood clotting. What I think this is does, and there is reasonable evidence about this, is that it increases the risk of having a thrombosis and the two main categories of event which we know arise are strokes and heart attacks and both of them have thrombosis at their heart, that is for a heart attack it is where a blood clot forms on a roughened artery in the coronary circulation of the heart and a stroke, or many strokes, occur because of a blood clot or thrombosis occurring on arteries to the brain.

So I think one major source of the mortality is because of that clotting mechanism which is really a function of the changes in circulation because of exposure to cold.

Dr Paul Wilkinson.

Bill, coincidentally I was reading this morning about a pilot study by the Met Office looking at the effects of cold snaps on COPD, that's emphysema and chronic bronchitis. Evidently hospital admissions peak 12 days after a cold snap and using an early warning system from the MET and giving COPD sufferers preventative advice, such as upping their medicines, researchers have managed to cut admissions - although I hasten to add the work has yet been published.

I suppose this is no surprise to you?

No we do see a very definite link between cold weather and deaths from respiratory disease. There's a delay of about 12-14 days where you get the peak of deaths after it. And there are various reasons for it. But yes it is - it's certainly desirable if possible to treat them beforehand. I think probably the main message is that at a time when the hospitals are under pressure in winter it's useful if the GPs can basically treat COPD patients early if they develop symptoms, if they get worse, and low temperature will be a warning that they're likely to ...

Likely to get worse. We heard there talk about outdoor temperature but presumably it's indoor temperature that matters more is it - because people if they're elderly, even if it's relatively mild outside if you're poorly dressed and immobile you can still be too cold I suppose?

Well yes you can indeed and in fact the clue to that or the key to it is really clothing because outdoor exposure is very important as well, as well as warm housing. And in fact you can get away to a degree with cooler housing if you're wearing long johns and sweaters and generally dressed up as people used to be in earlier times. But the most dramatic sort of example of this is that people indoors in Finland where they have very cold winters have less winter mortality than people in Athens, it is just because they know what to do in cold weather and they keep warm. And in Eastern Siberia the people of Yakutsk, it's the coldest city in the world, they have no winter mortality, although the temperature goes down to minus 50 and minus 60 in winter and they have massive fur clothing, they spend quite a bit of time outdoors in it but as long as they're really geared up for the weather they don't - they have less winter mortality than we do.

Bill, as my mother used to say to me, there's no such thing as bad weather just wrong clothes. That's all we have time for. Thank you very much.

Just time to tell you about next week's programme, which is on the kidneys - in particular why the NHS is having to deal with rising numbers of patients with kidney failure, a condition that already affects nearly 150,000 people across the UK.


Back to main page
Listen Live
Audio Help
Leading Edge
Emergency Services
Heart Attacks
Cot Death
Antibiotics and Probiotics
Bariatric Surgery
Backs - Slipped Discs
Prostate Cancer
Sun and Skin
Bowel Cancer
Cystic Fibrosis
Side Effects
Metabolic Syndrome
Down's Syndrome
The Voice
Childhood Burns
Sexual Problems
Me and My Op
Lung Cancer and Smoking
Cervical Cancer
Caesarean Sections
The Nose
Multiple Sclerosis
Palliative Care
Blood Pressure
Parkinson's Disease
Head Injuries
Tropical Health
Arts and Health 
Menopause and Osteoporosis
Intensive Care (ICU)
Manic Depression
The Bowel
The Jaw
Keyhole Surgery
Out of Hours
Body Temperature
Face Transplants
Heart Failure
The Royal Marsden Hospital
Cosmetic Surgery
Tired All The Time (TATT)
Coronary Artery Surgery
Choice in the NHS
Back to School
Hearing and Balance
First Aid
Alder Hey Hospital - Children's Health
Moorfields Eye Hospital
Wound Healing
Joint Replacements
Premature Babies
Prison Medicine
Respiratory Medicine
Urinary Incontinence
The Waiting Game
Auto-immune Diseases
Prescribing Drugs
Get Fit and Get Well Food
Oral Health
Heart Attacks
Genetic Screening
A+E & Triage
Screening Tests
Sexual Health

Back to Latest Programme
Health & Wellbeing Programmes
Current Programmes
Archived Programmes

News & Current Affairs | Arts & Drama | Comedy & Quizzes | Science | Religion & Ethics | History | Factual

Back to top

About the BBC | Help | Terms of Use | Privacy & Cookies Policy