The common cold
Common cold is the most common disease.
Common cold infections are so widespread that there can be very few humans who escape infection each year and most will suffer multiple infections. It has been estimated that adults suffer 2 to 5 colds per year, and school children may suffer 7 to 10 colds per year1.
As we get older we get fewer colds
As we get older our immune system learns how to deal with more and more viruses as we generate antibodies each time we get a cold.
Can a cold kill you?
Yes! Babies and the very elderly can develop chest infections such as bronchiolitis caused by the RSV virus that can be fatal. You are also at risk if you take any medication that depresses your immune system.
Viruses travel in style
Similar viruses are found in both the southern and northern hemispheres and in temperate and tropical climates and this is because cold viruses are as mobile as their host and readily jump from one continent to another by jumbo jet.
The densely populated cities of the modern world provide ideal breeding grounds for common cold viruses. Modern transport systems whisk viruses around from city to city.
Infection usually occurs at home
Young children represent the main reservoir of common cold viruses and infection usually occurs at home or in the nursery or school. Adults with regular contact with children are most exposed to infection.
Common cold viruses are not very contagious
Despite the fact that very few of us escape from at least a couple of common cold infections each year, common cold viruses are not very contagious. Under laboratory conditions when healthy volunteers are kept with others who are suffering from common cold infections it has proven remarkably difficult to spread infection from one person to another 2.
Kissing is OK
Close personal contact is necessary for the virus to spread and the home and school are the places where spread most often occurs. The common cold viruses are not spread by contact such as kissing but appear to be spread by large particles expelled at close range by coughs and sneezes, and by contaminated fingers that pass the virus to the nose and eye.
Your fingers can easily become contaminated with viruses by touching door handles etc. in public places. You may then touch your nose or eye and infect yourself. Tears from the eye drain via a duct into the nasal cavity and when we touch our eyes with contaminated fingers we pass viruses into the nose.3
How to avoid catching a cold
Become a hermit. If you are in contact with other people you are likely to get a cold as the viruses are so common.
Hand washing may help
Since cold viruses can be passed from person to person by hand contact or by touching contaminated surfaces such as door handles you can help prevent infection by washing your hands. Home studies have shown that hand washing can reduce the spread of common colds within the family4
When am I most infectious?
The incubation period for a common cold is usually around two days before symptoms start. You are most infective when you have the early symptoms of sneezing, runny nose and cough. The viruses replicate in the cells lining the nose and they are coughed or sneezed out in droplets of mucus.
We can also spread the virus on our fingers when we contaminate them with secretions from the nose. In order for you to spread the infection you need to have close and prolonged contact with other people and to cough or sneeze on them or pass on secretions from your nose via your hands.
The colds season
Colds occur all year round but there is an increased incidence during autumn and winter months.
Can a chill cause a cold?
Folklore indicates that chilling such as getting your feet wet in winter and going out with wet hair may cause a common cold but until recently there has been no scientific research to support this idea. Recent research has demonstrated that chilling may cause the onset of common cold symptoms.5
A study at the Common Cold Centre in 2005 took 90 students and chilled their feet in cold water for 20 minutes and showed that the chilled group had twice as many colds over the next 5 days as a control group of 90 students whose feet were not chilled.
The authors propose that when colds are circulating in the community some persons carry the virus without symptoms and that chilling the feet causes a constriction of blood vessels in the nose and this inhibits the immune response and defences in the nose and allows the virus to replicate and cause cold symptoms. The chilled person believes they have caught a cold but in fact the virus was already present in the nose but not causing symptoms.
Why more colds when its cold?
Colds and flu are definitely seasonal, with more colds in the colder weather but there is no real agreement as to why colds are seasonal.
Most textbooks state that there are more colds in cold weather because we tend to crowd indoors in poorly ventilated rooms. This crowding theory has been around for over a hundred years but it does not really make sense, as our cities are just as crowded in summer as winter.
A new theory that has been put forward to explain the seasonality of colds and flu, and this theory puts forward the idea that our noses are colder in winter than summer and that cooling of the nose lowers resistance to infection. If the weather is freezing outside we wrap up in winter clothes but we still leave our nose exposed to the freezing air.
Every time we breathe in we cool the nasal lining and weaken our local defences against infection. If this theory is correct then covering our nose with a scarf in cold weather could help prevent colds.6
1. Johnston S, Holgate S. Epidemiology of viral respiratory infections. In: Myint S, Taylor-Robinson D, eds. Viral and other infections of the human respiratory tract. London: Chapman & Hall, 1996:1-38.
2. Andrewes C. The Common Cold. New York: Norton, 1965:187.
3. Mygind N, Gwaltney JM, Jr., Winther B, Hendley JO. The common cold and its relationship to rhinitis, sinusitis, otitis media and asthma. In: Johnston S, Papadopoulos N, eds. Lung biology in health and disease. Respiratory infections in allergy and asthma. Vol. 178. New York: Marcel Dekker Inc., 2003:529-565.
4. Gwaltney JM, Moskalski PB, Hendley JO. Interruption of experimental rhinovirus transmission. The Journal of Infectious diseases 1980; 142:811-815.
5. Johnson C, Eccles R. (2005) Acute cooling of the feet and the onset of common cold symptoms. Family Practice 22: 608-613.
6. Eccles R. An explanation for the seasonality of acute upper respiratory tract viral infections. Acta Otolaryngologica (Stockholm) 2002; 122:183-191.