The nose contains shelf-like structures called turbinates, which help trap particles entering the nasal passages. Material deposited in the nose is transported by ciliary action to the back of the throat in 10-15 minutes. Cold viruses are believed to be carried to the back of the throat where they are deposited in the area of the adenoid. The adenoid is a lymph gland structure that contains cells to which cold viruses attach
A common cold is an illness caused by a virus infection located in the nose. (1) Colds also involve the sinuses, ears, and bronchial tubes.
The symptoms of a common cold include sneezing, runny nose, nasal obstruction, sore or scratchy throat, cough, hoarseness, and mild general symptoms like headache, feverishness, chilliness, and not feeling well in general. (1, 2)
Colds last on average for one week. Mild colds may last only 2 or 3 days while severe colds may last for up to 2 weeks.(1, 2)
A cold is a milder illness than influenza. Influenza typically causes fever, muscle aches, and a more severe cough. However, mild cases of influenza are similar to colds. (3)
Adults average 2 to 3 colds per year and children 6 to 10, depending on their age and exposure. Children's noses are the major source of cold viruses. (4)
There are over 100 different cold viruses. Rhinoviruses are the most important and cause at least one-half of colds. (5)
Cold viruses can only multiply when they are inside of living cells. When on an environmental surface, cold viruses cannot multiply. However, they are still infectious if they are transported from an environmental site into the nose. (6, 7)
Cold viruses live only in the noses of humans and not in animals except chimpanzees and other higher primates. (4)
A cold virus is deposited into the front of the nasal passages by contaminated fingers or by droplets from coughs and sneezes. (7) Small doses of virus (1-30 particles) are sufficient to produce infection. (8, 9)
The virus is then transported to the back of the nose and onto the adenoid area by the nose itself!
The virus then attaches to a receptor (ICAM-1) which is located on the surface of nasal cells. (11) The receptor fits into a docking port on the surface of the virus. Large amounts of virus receptor are present on cells of the adenoid. (12)
After attachment to the receptor, virus is taken into the cell where it starts an infection. (5) New virus particles are produced in the infected cell. The infected cell eventually dies and ruptures, releasing newly made cold virus to infect other cells in the nose and start the process over again. The virus is much smaller than the cell.
Small doses of virus (1-30 virus particles) when introduced into the nose are sufficient to reliably produce infection. (8, 9)
From the time a cold virus enters the nose, it takes 8-12 hours for the viral reproductive cycle to be completed and for new cold virus to be released in nasal secretions. (13) This interval is called the incubation period.
Cold symptoms can also begin shortly after virus is first produced in the nose (10-12 hours). (13) The time from the beginning of the infection to the peak of symptoms is typically 36-72 hours. (1, 2)
Myth 1:
The greatest myth about the common cold is that susceptibility to colds requires a weakened immune system.
Facts:
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 3:
Becoming cold or chilled leads to catching a cold.
Facts:
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)