Contagious diseases like cold and Flu are caused by the viruses present in the air. These are the contagious diseases that we easily get from others. (Usually they attack us in winter). The reason is; whether it is office or home, we shut all the doors and windows in that season and remain in-door. We all then breathe in what we have breathed out, and help the spread of viruses. In such cold winter days, if we keep all the windows open and let the air freely, cold will not attack us so easily.