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.
The common cold is spread when you inhale virus particles from an infected person’s sneeze, cough, speech, or loose particles from when they wipe their nose. You can also pick up the virus by touching a contaminated surface that an infected individual has touched. Common areas include doorknobs, telephones, children’s toys, and towels. According to the National Institute of Allergy and Infectious Diseases (NIAID), rhinoviruses (which cause the most colds) can live up to three hours on hard surfaces and hands.
Of the known viruses, most can be classified into a handful of groups, including human rhinoviruses, coronaviruses, parainfluenza viruses, and adenoviruses. 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.
In the United States, colds are more common in the fall and winter. This is mostly due to factors such as the start of the school year and the tendency for people to remain indoors. Inside, air tends to be drier. This dries up the nasal passages, which can lead to greater risk for infection. Humidity levels also tend to be lower in colder weather; cold viruses are better able to survive in low humidity conditions.
Human Rhinoviruses (HRVs)
This group of virus—of which there are more than 100 types—is by far the most common identified cause of colds. According to the National Institute of Allergy and Infectious Diseases (NIAID), this group causes about 30 to 50 percent of colds. They also grow best at the temperature inside the human nose.
Human rhinoviruses (HRVs) are highly contagious. However, they rarely lead to serious health consequences.
Recent research has found that the HRV manipulates genes and that it is this manipulation that brings about an overblown immune response—the response that causes some of the most troublesome cold symptoms. This information could lead scientists to important breakthroughs in the treatment forfg the common cold.
Though there are many varieties of coronavirus that affect animals, according to NIAID only five of the varieties infect humans. After rhinoviruses, this group of virus is the second leading known cause of the common cold. NIAID estimates that this group causes 10 to 15 percent of adult colds.
SARS (severe acute respiratory syndrome) is caused by a species of coronavirus, although not by one that can cause the common cold.
Human Parainfluenza Viruses (HPIVs), Adenoviruses, and Respiratory Syncytial Virus (RSV)
These three groups of viruses typically lead to mild infections in adults, but may lead to severe lower respiratory tract infections in children, the elderly, and those with weakened immune systems. Premature babies, children with asthma, and those with lung or heart conditions are at greater risk for developing complications such as bronchitis and pneumonia.
One strand of HPIV, HPIV-1 causes croup in children. Croup is characterized by the loud, startling sound that is produced when the infected individual coughs. The CDC has also found that military recruits are at greater risk for contracting adenoviruses that develop into respiratory illnesses.
20 to 30 percent of adult colds have unidentified causes although they are thought to be viral in origin, according to NIAID.