The cold is a common infection of the upper respiratory tract. Although many people think you can catch a cold by not dressing warmly enough in the winter, it is a myth that you can catch the common cold from exposure to chilly weather. The real culprit is one of more than 200 viruses. Of the known viruses, most can be classified into a handful of groups, including human rhinoviruses, cornoaviruses, adenoviruses, and parainfluenza viruses. Some other common cold culprits have been singled out, such as the respiratory syncytial virus. Still others have yet to be identified by modern science.

Human Rhinoviruses (HRV)

This group of virus is by far the most common identified cause of colds – it causes about 30 to 35 percent of colds – and is highly contagious. But rhinoviruses rarely lead to serious health consequences. Rhinoviruses – and there are over 100 varieties – tend to circulate in fall as well as spring and summer. Recent research has found that the HRV Virus manipulates genes and it is that manipulation that brings about an overblown immune response causing some of the most troublesome cold symptoms. This information could lead scientists to important breakthroughs in the war against the common cold.

Coronaviruses

Though there are about 30 total varieties of coronavirus, only three or four of the varieties infect humans. After rhinoviruses, this group of virus is the second leading known cause of the common cold. SARS (severe acute respiratory syndrome) is also caused by a species of coronavirus, although not by one that can cause the common cold.

Human Parainfluenza Viruses (HPIVs) and Respiratory Syncytial Virus (RSV)

These two groups of viruses lead to mild infections in adults, but children can contract severe lower respiratory tract infections. Both are common in young children. One strand of HPIV, HPIV-1, causes croup in children, for example. The elderly and those with compromised immune systems are at risk for complications like pneumonia and bronchitis. The same is true for adenoviruses, and again, there are many varieties.

Unidentified Viruses

30 to 50 percent of adult colds have unidentified causes although they are thought to be viral in origin. These unidentified viruses likely cause colds in children too, experts believe.