A common cold is a viral infection that primarily affects the upper respiratory system, including the nose and throat. Symptoms often include a runny or stuffy nose, sore throat, cough, sneezing, and mild fatigue. The illness is usually mild and resolves within a week or two without the need for medical treatment. Colds are caused by various viruses, with the most common being the rhinovirus. They are easily spread through respiratory droplets when an infected person coughs or sneezes, or by touching contaminated surfaces. While there is no cure for the common cold, rest, hydration, and over-the-counter medications can help alleviate symptoms.