Coronaviruses are believed to cause a large percentage of all adult colds. They induce colds primarily in the winter and early spring. Of the more than 30 isolated strains, three or four infect humans. Although many people are convinced that a cold results from exposure to cold weather, or from getting chilled or overheated, these conditions in fact have little or no effect on the development or severity of a cold. How cold viruses cause disease.
Viruses cause infection by overcoming the body's complex defense system.
The body's first line of defense is mucus, produced by the membranes in the nose and throat. When a virus penetrates the mucus and enters a cell, it commandeers the protein-making machinery to manufacture new viruses, which, in turn, attack surrounding cells. Cold symptoms are probably the result of the body's immune response to the viral invasion. Virus-infected cells in the nose send out signals that recruit specialized white blood cells to the site of the infection. In turn, these cells emit a range of immune system chemicals such as kinins.