What is the most common sickness?

The most common sickness is the common cold. It is a viral infection of the nose and throat, which is caused by a number of different viruses. The common cold is spread through contact with an infected person or through the air. Symptoms of the common cold include a runny nose, sore throat, coughing, sneezing, and a fever. The common cold usually goes away on its own in a few days, but it can sometimes lead to more serious illnesses, such as pneumonia.