Common cold The common cold is a viral infectious disease that infects the upper respiratory system. It is also known as acute viral rhinopharyngitis and acute coryza. It is the most common infectious disease in humans and is mainly caused by coronaviruses or rhinoviruses. The common cold is contagious; it can be spread by air droplets from coughs and sneezes and by touching infected surfaces. It is contagious from 1–2 days before symptoms begin until the symptoms have stopped. Because there are more than 200 viruses that cause the common cold, the human body can never build up resistance to all of them. This is why colds are so common and often return. Common cold symptoms include dry or sore throat, blocked or runny nose, and sneezing. Around a quarter of people do not experience symptoms when infected with a cold. Complications of the common cold include acute bronchitis and pneumonia People with lung conditions such as asthma and chronic obstructive pulmonary disease are more vulnerable to colds than other people. Return