No one looks forward to winter when cold viruses circulate more, and we spend more time indoors, where they spread more easily. Mostly, the common cold is a nuisance that stays around for a week or so and disappears. However, some upper respiratory viruses leave you with a dry cough that persists even after the cold leaves. Colds are caused by one of a variety of viruses that infect cells in the upper respiratory tract, and so far there is no cure. The best defense? Keep your immune system healthy, wash your hands, and avoid sick people. Practice healthy lifestyle habits too! One lifestyle habit that can benefit your immune system is exercise. Is there evidence that exercise can prevent the common cold? Here, David Reagan, an Atlanta-based personal trainer, answers this question in detail.