According to the National Institutes of Health (NIH), more than one billion colds are "caught" each year. Although it is considered to be a minor infection of the nose and throat caused by a virus, it is the leading cause of school and work absences, as stated by eMedTV. The symptoms typically begin with one or two days of catching the virus, they can last up to two weeks, with its sufferer being contagious the entire time.
The general cause of nasal congestion is a virus. This virus may be the underlying cause of the cold symptoms many experience. Also called a stuffy nose, nasal congestion is a result of the swelling that occurs in the tissues of the lining of the nose. This is a direct result of inflamed blood vessels, not an excess of mucus as some people believe.
Another symptom causing you to be contagious is nasal discharge, or a runny nose. This is only serious in rare cases, however in most, it is common. This typically occurs when swollen nasal cavities begin to drain. In many cases, the drainage is a thick mucus, and is generally green or yellow in color. Other cold symptoms, such as a persistent cough or sore throat, can occur due to a nasal drip down the back of your throat.
According to the NIH, sneezing is due to an irritation of the mucous membranes of the nose or throat. This symptom can easily spread the cold to others, especially when the person sneezing does not cover his nose or mouth. It is then that the germs are spread through the air, waiting for someone healthy to inhale them.
Acute coughing begin suddenly and are another symptom of the common cold. There are two different types of cough which may both be contagious due to the spread of germs in the air: Productive and dry. A productive cough is one that brings up mucus, which is also called sputum or phlegm. And while coughing is your body's way of keeping your airways clear, when it is persistent, it is a sign of an underlying infection, such as a cold.