Common colds are caused by viruses, which can be spread through direct contact with an infected person or through the air, such as through sneezing or coughing. The most commonly identified virus causing colds is the rhinovirus, which is responsible for more than half of all colds. Other viruses that can cause colds include coronaviruses, respiratory syncytial virus (RSV), and adenoviruses.
In addition to viruses, bacteria can also cause colds. Bacteria that can cause colds include Streptococcus pneumoniae, Haemophilus influenzae, and Mycoplasma pneumoniae. These bacteria are usually spread through direct contact with an infected person or through the air.
Cold viruses and bacteria can also be spread through contact with surfaces that have been contaminated with an infectious agent, such as doorknobs or countertops. In this case, touching the contaminated surface and then touching the eyes, nose, or mouth can result in infection.
In addition to viruses and bacteria, other environmental factors can also increase the risk of getting a cold. These include exposure to cold weather, low humidity, cigarette smoke, and air pollution.
By taking preventive measures such as washing hands often, avoiding contact with people who are sick, avoiding touching the face, and getting a flu shot, people can reduce their risk of getting a cold.