Understanding Colds

Anatomy of the Nose

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.

Ciliary Action


Nose Anatomy


CAT Scan of the Nose and Sinuses

The maxillary sinus (black) is surrounded by bone (white). Soft tissue, such as the eye, is gray. The maxillary sinus of adults has a volume of 30 ml (2 tablespoons). Ciliary action moves sinus secretions up to the drainage passage, called the infundibulum. The drainage passage has a diameter the size of the lead in a pencil (3 mm). Mucus is moved out of the sinus cavity at the rate of 1 cm (3/8 inch) per minute.

Animated CAT Scan


Nose CAT Scan

What a Common Cold Is

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)

How Cold Virus Infection Occurs

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! (10)

Cold Virus Docking

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)

Cold Virus Infection

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)

What Causes Cold Symptoms

Cold viruses (rhinovirus) infect only a relatively small proportion of the cells lining the nose (see figure). (10, 14, 15) Membrane damage is mild.

Cold symptoms are due mainly to the body's response to the infection. When a nasal cell is infected by a cold virus, the body responds by activating parts of the immune system and some nervous system reflexes. (5)

The immune system contains a variety of natural substances called inflammatory mediators. Inflammatory mediators help protect the body from infection and other harmful events. Some inflammatory mediators are released when nasal cells are infected by a cold virus. The names of some inflammatory mediators involved in colds include histamine, kinins, interleukins, and the prostaglandins. (5, 16-19)

Micrograph of Infected Nasal Cell


When activated by a cold virus infection, inflammatory mediators cause dilatation and leakage of blood vessels and mucus gland secretion. (5) Inflammatory mediators also activate sneeze and cough reflexes and stimulate pain nerve fibers. These events are what lead to the symptoms of a cold.

The activity of the inflammatory mediators is not necessary for recovery from cold virus infection. Twenty-five percent of people who acquire cold virus infection do not develop symptoms. (4) People without cold symptoms recover from the infection as well as those who have symptoms.

The individual symptoms of a cold are caused by the action of particular inflammatory mediators, although there is some overlapping. (5) This has important implications for developing and selecting effective cold treatments.