Over 200 different viruses can cause the common cold resulting in a runny nose, cough, sore throat and headache, says the University of Maryland Medical Center. Viruses are easily transmitted from one person to another by droplet transmission. When an infected person coughs or sneezes, droplets can spray as far as 20 feet and can live for several minutes. If an individual breathes in those droplets, they can become infected. The virus is also transmitted on hands, so touching a door knob or desk, someone's keyboard or mouse, may give family members and co-workers more than they bargained for.
Virus particles that enter the nose become trapped in the nasal hairs and cilia inside the nasal passages. Chemical substances in the moist nasal lining will destroy some of the particles. Other virus particles invade the cells lining the back of the throat and upper airway. As the virus begins to replicate within the body's cells, hundreds of new virus particles are released to attack new cells and multiply. According to the University of Maryland Medical Center, "Researchers have found that the human rhinovirus can actually skip a step when it makes its protein product, a shortcut that speeds up its ability to make a person feel sick soon after infection."
As the virus continues to replicate and invade the cells, the body temperature begins to rise in an attempt to kill the virus, sometimes producing only a low-grade fever that may not even be noticed. As the affects of the invasion take place, an individual will now begin to feel ill. According to the University of Maryland Medical Center, some viruses mutate by making small changes in certain proteins to avoid being captured and destroyed by antibodies from a your immune system. The severity of colds brought on by viruses depends on the strain and how well your immune system can fight it.
Irritation caused by the virus particles cause sneezing, which expels some of the virus particles enabling someone else to become infected. The blood supply to the lining in the infected nasal passages increases, distributing large numbers of white blood cells called lymphocytes. The blood vessels become engorged, causing the nasal lining to produce fluid, starting a runny nose and eventually, congestion. The cold begins to run its course as an individual tries to relieve the symptoms with fever reducers and cough suppressants.
Some of the lymphocytes produce proteins called antibodies that immobilize the virus particles. Other lymphocytes secrete powerful chemicals that destroy contaminated cells along with the virus particles inside them. Other white blood cells called phagocytes swallow up and digest the immobilized, destroyed and damaged particles and cells, says the University of Maryland Medical Center. Within a week the symptoms begin to subside as the body gets the upper hand and continues to clear out the virus particles that have remained behind.