I'm thick...

Acute nasopharyngitis, often known as the common cold, is a mild viral infectious disease of the upper respiratory system (nose and throat). Symptoms include sneezing, sniffling, nasal congestion; scratchy, sore, or phlegmy throat; coughing; headache; and tiredness. Colds typically last three to five days, with residual coughing lasting up to three weeks. As its name suggests, it is the most common of all human diseases, infecting subjects at an average rate of slightly over one infection per year per person.

The common cold belongs to the upper respiratory tract infections. It is different from influenza, a more severe viral infection of the respiratory tract that shows the additional symptoms of rapidly rising fever, chills, and body and muscle aches. While the common cold itself is rarely life threatening, its complications, such as pneumonia, can very well be.

Transmission

The viruses are transmitted from person to person by droplets from coughs or sneezes. The droplets or droplet nuclei are either inhaled directly, or transmitted from hand to hand via handshakes or objects such as door knobs, and then introduced to the nasal passages when the hand touches the nose or eyes.

The virus takes advantage of sneezes and coughs to infect the next person before it is defeated by the body's immune system. Sneezes expel a significantly larger concentration of virus "cloud" than coughing. The "cloud" is partly invisible and falls at a rate slow enough to last for hours—with part of the droplet nuclei evaporating and leaving much smaller and invisible "droplet nuclei" in the air. Droplets from turbulent sneezing or coughing or hand contact also can last for hours on surfaces, although less virus can be recovered from porous surfaces such as wood or paper towel than non-porous surfaces such as a metal bar. A sufferer is most infectious within the first three days of the illness.

Symptoms

Ninety-five percent of people exposed to a cold virus become infected, although only 75% show symptoms. The symptoms start 1–2 days after infection. Generally a cold starts with a sore throat, without any respiratory blockage. From then onwards the symptoms are a result of the body's defense mechanisms: sneezes, runny nose, and coughs to expel the invader, and inflammation to attract and activate immune cells.

Prevention

The best way to avoid a cold is to avoid close contact with existing sufferers, to wash hands thoroughly and regularly, and to avoid touching the face. Anti-bacterial soaps have no effect on the cold virus - it is the mechanical action of hand washing that removes the virus particles. In 2002, the Centers for Disease Control and Prevention recommended alcohol based hand gels as an effective method for reducing infectious viruses on the hands. However, as with standard handwashing, alcohol gels provide no residual protection from re-infection. Tobacco smoking has also been linked with the weakening of the immune system; non-smokers are known on average to take fewer days off sick than the smoking population.