Why Don't Penguins' Feet Freeze?: And 114 Other Questions - Mick O'Hare (2009)

Chapter 2. Feeling OK?

8986 Catch your death

Is there any connection between being cold and catching a cold? If not, why is there so much folklore about catching a cold if you sleep uncovered or in a draught?

Antonis Papanestis

London, UK

No, there is no connection. The erroneous association developed for several reasons.

The viruses that cause colds spread faster in the winter because people spend more time inside, where they are closer together.

People close the windows in winter so air contaminated by virus particles is not diluted by ‘fresh’ air from the outdoors. This makes it easier for the virus to spread.

The cold, dry air of winter makes the mucous membranes in the nose swell. This produces the ‘runny nose’ we often incorrectly associate with an infection caused by a cold virus.

The experience of catching a chill and getting a cold is actually the reverse of the correct order of things. The chill is often the first sign of fever that is the result, not the cause of, the infection by the cold virus.

Mark Feldman

Northland, New Zealand

Studies have shown that there is no correlation between environmental temperature and suffering from colds. The origin of the old wives’ tale that predicts colds, ’flu or pneumonia after being exposed to cold temperatures is the short period of fever that precedes the distinctive symptoms of these illnesses. These periods of fever make the patient feel cold and shivery. Shortly after developing other symptoms, the patient then associates the illness with having ‘caught cold’. Indeed, the ’flu is called influenza from the belief that it was caused by the ‘influence’ of the elements. The fact that isolated researchers living in Antarctica never catch colds confirms that these are caught from people and not from ‘cold’.

Pedro Gonzalez-Fernandez

London, UK

There is actually less chance of your catching a cold in the cold. The virus known as the common cold dies in cold and needs warmth (say the cosy indoors of a home beside the fire started to keep out the cold) to thrive.


By email, no address supplied

8986 It’s not

Sorry, but I had to ask, why is nasal mucus often green?

David Tanner

Felsburg, Germany

Of all the body cavities in contact with the outside world, the nose is probably one of the most hospitable: it is warm, very well aerated, moist and supplies unlimited quantities of bacterial food secreted continuously by the nasal mucosa (mucus contains quantities of glycoprotein and dissolved salts). In other words it is an ideal breeding ground for bacteria, which are always present.

Many of the common bacteria associated with humans are coloured, Staphylococcus aureus is a golden yellow, for example, and Pseudomonas pyocyanea (to give it its older, but more explicit name) is a shade of blue. Normally these and the multitude of other organisms that are inhaled continuously into the nose are flushed out by runny mucus, which is swallowed. The bacteria are usually digested.

However, if a situation arises where the flow of mucus slows down and then becomes much thicker in response to an infection of any kind, then the bacteria, in their ideal home, can multiply and produce the coloured mucus described. This, as many parents know, is one of the less endearing characteristics of babies and young children!

And, by the way, if you’re still wondering where the green colour comes from, remember what happens when you add blue to yellow.

Laurie North

London, UK

Your previous correspondent suggested that the green colour is caused by a combination of golden-yellow Staphylococcus aureus and blue Pseudomonas pyocyanea. This is a rather tenacious belief. While the eighth edition of Bergey’s Manual of Determinative Bacteriology (Williams & Wilkins, Baltimore, 1974) still held P. pyocyanea ‘commonly isolated from wound, burn and urinary tract infections’ to be the causative agent of ‘blue pus’, the cause of the green colour of pus or nasal mucus is more general.

Green pus (or green nasal mucus) is caused by iron-containing myelo-peroxidases and other oxidases and peroxidases used by polymorphonuclear (PMN) granulocytes (neutrophils). These short-lived phagocytising leucocytes avidly ingest all sorts of bacteria and inactivate them by oxidative processes, involving the iron-containing enzymes above. The resulting breakdown product (comprising dead PMNs, digested bacteria and used enzymes), pus, contains significant amounts of iron, which gives it its greenish colour.

C. J. van Oss

Department of Microbiology

State University of New York, Buffalo, US


J. O. Naim

Department of Surgery

Rochester General Hospital, New York, US

Nasal mucus isn’t always green. Nasal mucus produced at the beginning of a cold is clear and is produced in response to tissue damage caused by the invading rhinovirus. It only turns green a few days into the infection as neutrophils respond to clear away the cellular debris and secondary bacterial infection sets in.

Juli Warder

Abingdon, Oxfordshire, UK

Polymorphonuclear leucocytes are equipped with a number of enzymes, the most potent of which is peroxidase. This same peroxidase is also found in horseradish, giving it a distinctive green colour and a sharp (if fleeting) bite, as anyone who has tried Japanese wasabi paste can confirm. English horseradish sauce loses its colour due to oxidation of this labile enzyme on exposure to air. However, authentic wasabi is always served fresh.

Sorry if this response puts some readers off their sushi.

Steve Flecknoe-Brown

Sydney, Australia

8986 Ouch!

What causes the pain induced by a piece of silver foil touching a tooth filling?

Simon Oddy

Melksham, Wiltshire, UK

The questioner is inadvertently replicating a famous experiment first performed by Luigi Galvani in 1762.

When two dissimilar metals are separated by a conducting liquid, a current will flow between them, and this current can be used to stimulate nerves.

This is exactly what happens when silver foil appears to touch the amalgam of a filling. A thin film of saliva actually separates foil from filling, and because saliva is a reasonable electrolyte, containing various salts, a current will flow between the tooth and the filling. As the filling is close to the dental nerve, the current will stimulate it, causing pain.

Galvani carried out his experiment with frogs’ legs and metal probes, but the effect was the same – they twitched!

Chris Quinn

Widnes, Cheshire, UK

8986 Speaker’s throat

What are the bodily changes that cause us to have a dry throat when we are nervous?

Howard Foss

Honiton, Devon, UK

You get a dry mouth during public speaking because when you are nervous the body is set into the ‘fight or flight’ state. This is caused by an activation of the autonomic nervous system. It is seen throughout the animal kingdom, and has evolved to help the animal deal with dangerous situations – when escaping from predators, for example.

The nerves are selectively activated, depending on how important they are for the response. Because eating is not considered to be important at this time – you want to get the hell out of the place – the nerves to your mouth that control the salivary glands are suppressed, so your mouth dries up. In addition, your pupils dilate and the blood vessels to your muscles and heart are enlarged in order to get the blood to the most important organs needed for whatever drastic action is necessary.

M. Scotten

By email, no address supplied

This is tied to the ‘fight or flight’ reaction. In a tense or dangerous situation, your body shuts down all unnecessary functions, including the digestive system. Your saliva glands are a part of it. You don’t need to digest your last meal if a lion is trying to make you his next. This is also where butterflies in the stomach come from.

Bill Isaacson

By email, no address supplied

8986 Light night

When you have a heavy cold, your nose runs all day but stops as soon as you fall asleep at night. What mechanism turns off the flow of mucus? Could a drug be developed to do the same and therefore alleviate the worst effect of the cold? And could such a drug also help to reduce the spread of colds?

Peter Rooney

Epsom, Surrey, UK

This phenomenon is merely a matter of gravity. When you settle down to go to sleep, the action of lying on your back means that the mucus being secreted in your nasal passages, rather than running down and out of your nose, instead travels towards the back of the throat where you swallow it unconsciously.

If you sleep on your side, just one nostril (the lower one) becomes blocked, and if you want to unblock your nose, it is usually sufficient merely to alter your orientation, so if lying down, stand up, and if standing up, lie down. This reverses the direction of the mucus flow and clears the blockage.

Alexandra McKenzie Johnston

Thirsk, North Yorkshire, UK

The runny nose that occurs while we’re awake is caused by head position. When we sleep, almost all the post-nasal drip drains down the throat because we are lying down, sometimes on our sides and sometimes on our backs. I suffer from this problem and, after testing my theory using a massage table that had a face-hole opening, I started using pillows to position my head so my nose points downhill.

Test it yourself using pillows, leaving a gap so that you can rest your head face down while leaving a space for your mouth and nose. Oh, and have some handkerchiefs ready: you’ll probably find that your nose runs copiously all night.

Hank Roberts

Berkeley, California, US

The questioner is mistaken in his belief that the runny discharge is contagious. Most colds are contagious from two to four days after exposure to the virus, which is usually before the symptoms appear. Once you start to suffer from a runny nose, the infection is well under control and the amount of virus present in the nasal secretion has diminished.

The most common way to catch a cold is through hand contact with the virus rather than from people with runny noses. Colds are more easily transmitted via a hard surface that other people have touched, such as a doorknob or computer mouse.

Instead of avoiding people with runny noses, it is far more important to make sure that you do not touch your eyes, nose or mouth with your hands after they have been in contact with various objects in either your home or your office.

David Gibson

Leeds, West Yorkshire, UK

8986 All in the mind

Discussion of the placebo effect in the testing of therapeutics always seems to focus on positive placebo effects. Are there negative placebo effects?

Peter Grant

South Australia

Placebos are substances with no pharmacological properties, such as sugar or dummy pills. They are widely used as a control in experiments to test the effect of medicines, and are made to look and smell the same as the drug being tested. Subjects are not told whether they are receiving the actual medicine or the placebo.

How the placebo effect works is still controversial, but it is widely believed that the effect is psychological rather than physiological: the benefit occurs because people believe that the pill they are taking should cause positive effects. The effect has also been attributed to conditioning: patients expecting the effects of a drug will then experience them.

Take the example of placebos used in tests on analgesic drugs. An explanation for the placebo mechanism in this case is that it involves the release of opiate-like pain-relieving chemicals in the brain. One study found that pain was reduced by a placebo medication that the patients believed was a pain reliever, but that the effect ceased when the patients were given a drug that counteracts the effect of opiates.

The negative effects of placebos are called nocebo effects, nocebo being Latin for ‘I will harm’. Patients receiving dummy pills sometimes experience side effects such as anxiety and depression. This is thought to be associated with the person’s expectations of adverse effects of the treatment as well as conditioning. It was reported in one trial that women who believed they were prone to heart disease were nearly four times as likely to die from heart disease as women with similar risk factors who had no such belief.

Placebos pose an ethical dilemma. They work primarily by a doctor deceiving their patient into believing that they are receiving an active medicine, while in fact depriving them of any such medicine. If they also suffer nasty side effects through the nocebo effect, this arguably makes things worse.

Ian Smith

London, UK

Yes, there are negative placebo effects, or nocebo effects. Nocebos, like placebos, cause a physical effect, though not primarily through a physical mechanism. It seems likely that their effect comes from the patient’s belief. It’s ‘think sick, be sick’ for the nocebo, as opposed to ‘think well, be well’ for the placebo.

The kind of patient most likely to experience the nocebo effect of a given drug has a history of vague, difficult-to-diagnose complaints and is sure that whatever therapy is prescribed will do little to battle the problem. Those low expectations are inevitably met. The nocebo effect also affects the outcome of operations. Surgeons are wary of people who are convinced that they will die. Studies have been carried out on people undergoing surgery who say that they wish to die to be reunited with a loved one. Almost all of these people do die.

There is very little research on nocebos, mostly for the ethical reason that physicians ought not to induce illness in patients who are not sick. And changing ethical standards have made it difficult to even repeat some of the classic nocebo experiments. The most recent medical review article on nocebo effects was published in 2002 by Arthur Barsky and others (The Journal of the American Medical Association, volume 287, page 622).

Ross Firestone

Winnetka, Illinois, US

There are negative placebo effects. Their best-known manifestations are voodoo, and other ‘magical thinking’ that involves curses. Such practices almost invariably include some mechanism for letting the victim know that he or she has been cursed, and this is the main, possibly only, requirement for success.

Steven Reitci

West Allis, Wisconsin, US

8986 Expect pain in knee area

I damaged my knee ligaments in a skiing accident about two years ago. Ever since then I have had what I describe as a ‘weather forecasting knee’. Before it rains I always experience pain in my knee. This happens in both summer and winter and does not seem to be related to humidity. I am not the only person to have reported this. Why does my knee hurt before it rains and, more interestingly, how does it know? How does it detect the onset of rain?

Debbie Reid

Chalfont St Giles, Buckinghamshire, UK

Plenty of studies have looked at pain associated with weather, especially in people suffering from arthritis. These show that there is a real effect, but oddly there has been little research into what causes the pain – Ed.

The human body can be viewed schematically as a clump of gelatin-filled balloons mounted on a stick. Undamaged tissue – be it fat, muscle, or bone – is relatively elastic and will expand and contract when subjected to changes in atmospheric pressure. Scar tissue, in contrast, is very stiff and dense, and does not expand or contract appreciably within the range of normal atmospheric fluctuation.

Imagine if several of the balloons in your hypothetical body clump were glued together and then the surrounding pressure was lowered. The balloons would expand, so the glued-together area – representing the scar tissue – would distort and pull as a result, which in living tissue results in nerve stimulation and a rapid onset of pain. This persists until the pressure normalises or the scar eventually stretches to relieve the distortion. This may take hours or days.

I occasionally mystify my office staff by announcing in the morning: ‘It’s going to be a busy day for drop-in patients.’ They never know how I can predict the 20 or 30 who will call with a severe increase in pain from surgery or an old injury. I’d rather my staff think I have magical abilities than confess I read the weather report.

Immersion in a hot tub and gentle exercise may ease the pain. Waiting for the weather to change works too, and here in east Texas that usually happens before you can fill the tub.

Steven Ballinger

Nacogdoches, Texas, US

It may sound like an old wives’ tale that wet weather aggravates arthritis, but in the 1960s a rheumatologist called Joseph Hollander built an experimental climate chamber to test the claim. He found that high humidity combined with low barometric pressure – the meteorological situation before it rains – is indeed associated with joint pain or stiffness.

One explanation is that the change in weather makes injured ligaments swell, and the nerves around the joint sense this as pain. Another is that air within the joint may expand when barometric pressure drops, again causing the nerves to report pain.

A recent experiment by Japanese scientists demonstrated that back pain associated with changes in barometric pressure is linked to the vacuum phenomenon, in which gases build up in the spaces between the vertebrae (Journal of Spinal Disorders and Techniques, volume 15, page 290). Such bubbles form as the discs between the vertebrae deteriorate, and are more common in older people. They can also form in other joints. Avoid pain by keeping your knee dry and warm. And, of course, you are now more qualified than most to work as a local TV weather forecaster.

Frank Wong

Sydney, Australia

One explanation for the weather-predicting knee is ‘bone bruising’ – bleeding and oedema caused by microscopic fractures of trabecular, or porous, bone. Some studies have found these are relatively common after ligament injury to the knee.

Maybe changes in atmospheric pressure could change the volume of the oedema in the bone and produce pain. If so, two predictions might be made: an MRI scan will show bone bruising, and the patient’s ability to predict weather should decrease as the injury heals.

Peter Hallas

Copenhagen, Denmark