The common cold is a viral infection that affects the upper respiratory system, including the nose and throat. It's characterized by symptoms such as sneezing, runny or stuffy nose, cough, and sometimes a sore throat. The common cold is very contagious and can be spread through contact with infected individuals, touching surfaces contaminated with the virus, or inhaling viral particles from the air. While most people recover from the common cold within a week or two, some symptoms may linger longer.