Although cold symptoms can make you miserable - such as coughs, runny noses, and stuffy noses - they tend not to be serious. In most cases, they are caused by viruses, and they get better with time and rest. A viral infection can cause symptoms that last up to 14 days, sometimes even longer. It usually takes about 10 days for the worst to pass, although a cough may last three weeks in some cases. You are contagious for a certain period of time after having a viral infection, depending on the virus. It is often possible to spread the infection before you start feeling unwell.