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Myths of the Common Cold

Myth 1: The greatest myth about the common cold is that susceptibility to colds requires a weakened immune system.


  1. Healthy people with normal immune systems are highly susceptible to cold virus infection once the virus enters the nose. In volunteers studies, approximately 95% of normal adults became infected when virus was dropped into the nose (72, also see How Cold Virus Infection Occurs).
  2. Of people who become infected, only 75% develop symptoms with a cold. (5, 72) The other 25% have virus growing in the nose but have no symptoms. They have an "asymptomatic infection".
  3. Why people sometimes become infected but do not develop cold symptoms is a mystery. One clue is that in such instances the person may not be producing the normal amount of certain inflammatory mediators, the natural body chemicals which cause cold symptoms (2, also see What Causes Cold Symptoms). If this theory is correct, then people with active immune systems may be more prone to developing cold symptoms than people with less active immune systems!

Myth 2: Central heating dries the mucus membranes of the nose and makes a person more susceptible to catching a cold.


  1. As discussed above, a cold virus does not need the help of dry mucus membranes to initiate a cold once it enters the nose (72, also see How Cold Virus Infection Occurs).
  2. The nasal mucus membrane is very resistant to the effects of low humidity. Volunteers placed in chambers where the humidity was dramatically lowered (9% relative humidity, such as found in a desert) still have normal clearance function of the nasal mucus membrane. (73, 74) Low humidity makes the nose feel dry but the mucus membrane still continues to work normally.
  3. The cold season in the United States typically begins in late August and early September at a time when temperatures are still moderate and central heating is not being used. (74, 75) September is the time of a major common cold epidemic despite people not being exposed to the drying effects of central heating.

Myth 3: Becoming cold or chilled leads to catching a cold.


  1. As discussed above, almost everybody becomes infected whether they are chilled or not, if cold virus is dropped into the nose. (72)
  2. One study has looked at this question. It was found that colds were no more frequent or severe in volunteers who were chilled than those who were not. (76)

Myth 4: Having cold symptoms is good for you because they help you get over a cold, therefore you should not treat a cold.


  1. Approximately 25% of people who get a cold virus infection do not develop symptoms and yet they get over the infection as well as people who do have symptoms (5, 72, also see How Virus Infection Occurs).
  2. The nose can only respond to irritative events such as a cold virus infection or dust or pollen entering the nose in a limited number of ways. Sneezing and nasal secretions are useful in removing dust and pollen from the nose but do not eliminate cold viruses since the virus is multiplying inside the nasal cells where it is safe.
  3. Nose blowing propels nasal secretions into the sinus cavity. (41) Nasal secretions contain viruses, bacteria, and inflammatory mediators all of which are able to produce inflammation in the sinus cavity. This may lead to secondary bacterial infection.
  4. Nose blowing, sneezing, and coughing benefit the virus by helping spread it to other people (see How Colds are Spread).
  5. Commercially available and FDA approved cold treatments are safe and effective (see Treatment). It makes sense to use them because they benefit the cold sufferer and may help prevent the spread of colds.

Myth 5: Drinking milk causes increased nasal mucus during a cold.


  1. Milk and mucus may look alike, but milk is digested like any other protein and is not specifically converted into nasal mucus.
  2. An Australian study was actually done in volunteers to address this question. (77) It showed that people drinking lots of milk had no more nasal mucus than those not drinking milk.


Myth 6: You should feed a cold (and starve a fever).


  1. The origin of this old saying is obscure. There is no scientific evidence that excess eating will cure a cold.
  2. On the other hand, eating tasty food will not make a cold worse and may help the cold victim feel better. Commoncold.org features the following tasty recipes for the cold sufferer.


Feed A Cold Recipes

These recipes are provided as PDF files for ease of printing:


Testing Cold Treatments

New cold treatment ideas require testing in clinical trials to determine if they actually work. Testing is necessary because of four natural circumstances effecting the nature of colds:

  1. Colds are a self-limited illness from which virtually all people recover in a few days. (1) If colds were universally fatal, no formal testing of new treatment ideas would be necessary to determine if they work.
  2. The duration and severity of a cold varies from one person to another and also varies in the same individual over time. (2) If all colds were exactly alike in all people at all times, it would also not be necessary to perform clinical trials on new treatment ideas.
  3. Colds respond to placebo (sugar pills). (69) People given totally inactive substances such as small amounts of starch as a "treatment" will have significantly milder illnesses than those who are given no "treatment." Interesting examples are available of how curious subjects in clinical trials have sometimes been able to guess correctly about whether they were on the experimental drug or placebo and thus unblinded themselves. (70)
  4. The benefit of most effective treatments for most self-limited diseases are not so dramatic that it is always obvious that the treatment is effective in an individual case.

For these reasons, an individual taking a cold treatment based on the new idea may be mislead into believing the experimental treatment was effective because the cold being treated was naturally mild or because the person experienced a placebo reaction or both. Conversely, a person trying a new treatment idea might be misled into believing it did not work when actually it did provide some benefit, but the benefit was obscured by the patient having a particularly severe cold.

To accurately test the value of new cold treatment ideas requires conducting experiments in which these chance events and biases are adequately controlled. (71) Chance and bias can never be totally eliminated from a testing situation. The experimental design which most effectively reduces the influence of chance and bias is that of a properly "powered", "controlled", "randomized", "double blinded" clinical trial.

"Controlled" means that the treatment idea being tested is compared to either placebo (inactive substance, sugar pill) or to another treatment which has previously been shown to be effective. (71) Comparison to a placebo determines if the new treatment has any benefit at all. Comparison to a new treatment determines if the new treatment is better than the old one.

It is important that a clinical trial have enough subjects enrolled to give accurate results. This is called having adequate "statistical power". (71) It would not make sense to have only one or two people in each group of a clinical trial because people naturally vary in the length and severity of their colds. It would also not make sense to have 100,000 people in each group because a study of this size would be difficult and expensive to conduct. More importantly, an accurate answer to the question could be obtained with much fewer subjects. It would be a waste of resources. Mathematical calculations can be used to select the correct number of subjects ("sample size") for a particular clinical trial, depending on its purpose.

"Double blinded" ("masked") means that neither the investigator conducting the clinical trial nor the subjects in the trial know who is getting the experimental treatment and who is getting the placebo (or the older treatment). (71) Masking controls for the bias associated with the placebo effect and for any biases on the part of the investigator or subjects, who naturally would like to see a new idea for treatment succeed. Being biased does not mean that a person is dishonest. However, masking also helps control for any dishonesty on the part of the investigator, if such is present.

"Randomized" means that subjects are assigned to either the group receiving the experimental treatment or the control group (receiving placebo or comparator drug) in a random fashion, such as by flipping a coin. (71) Randomization also helps control for a bias such as might occur if most of the sicker cases were assigned to one group. If this happened, the test material given to the sicker group would not look as effective as that given to the group with milder illness.

What to Look for in Evaluating New Cold Treatment Ideas

  1. Do the investigators have a reputation for honesty and competency? This may be difficult or impossible to determine.
  2. Was the new treatment idea tested in a clinical trial?
  3. Were the results of the trial published in a "peer reviewed" medical journal? "Peer review" means that the paper was evaluated and approved by independent experts before it was accepted for publication.
  4. Was the clinical trial controlled? (71) Was it designed so that the new treatment was compared to placebo or an established form of treatment?
  5. Were "sample size" calculations done to determine that the study had adequate statistical power? Does the paper state what specific endpoints were being evaluated and why the number of subjects assigned to the treatment and control group was selected?
  6. Did the clinical trial have a double blinded design? Were both the investigators and the subjects unaware of what was being given to the subjects until after the study was completed?
  7. Was there proof that the new drug preparation (tablet, capsule, liquid, etc.) was indistinguishable from the placebo or comparator drug preparation? Was actual testing done to determine that people could not distinguish the new drug preparation from the placebo or comparator drug before the clinical trial was conducted? Were the preparations compared for such things as appearance, smell, taste, after-taste, and any other characteristics that might help subjects to guess whether they were receiving the experimental treatment or the control preparation?
  8. Were subjects randomly assigned to the treatment and the control group? This is usually done by a table of random numbers or a computer-generated list of random numbers.
  9. Have the investigators carefully looked for and reported the side effects of the experimental treatment?

If the evaluation of a new cold treatment idea meets these nine criteria, you can feel confident that it has been properly tested and that the results of the study are probably correct ("valid"). It is even better if other investigators had done clinical trials with the same experimental treatment and have obtained similar results. In general, the Food and Drug Administration requires three well done clinical trial before recognizing a new treatment as being effective.

It is important to appreciate that a clinical trial of a cold treatment represents actual testing of the treatment in real people with colds. Theoretical reasons that are given to support the contention that a new cold treatment works such as it "boosts the immune system" are no substitute for a real clinical trial. The history of medicine shows that untested treatment claims based on theory are often misleading. The immune system of humans is very complex and much of it has nothing to do with preventing colds. Healthy people with normal immune systems are very susceptible to infection when a cold virus is introduced into the nose (see How Cold Virus Infection Occurs). There is also some evidence that cold symptoms occur because the immune system is working well and actively producing inflammatory mediators, which are the cause of cold symptoms (see What Causes Cold Symptoms). The latter theory is exactly the opposite of the myth of a weakened immune system leading to colds and of using cold treatments which "boost the immune system" (see Myths of the Common Cold).

A claim that a new cold treatment idea is effective raises four possibilities:

  1. The treatment idea has been properly tested and shown to work.
  2. The treatment idea has not been properly tested. The one making the claim, though well meaning, does not understand the importance of clinical trials.
  3. The treatment idea has been properly tested and shown not to work or has not been properly tested. Someone is trying to defraud the public.
  4. The treatment idea has not been properly tested. Someone is the recipient of supernatural revelation.