Colds are a type of upper respiratory tract infection, caused by viral infections that can be combined with or secondary to bacterial infections. In general when pathogens enter the body, the body will have an immune defense line against it, if the person’s immunity is poor, it is easy to trigger cold symptoms, if the person’s immunity is relatively strong, pathogens are the immune system to remove in time is not enough to cause disease, at this time will not appear obvious symptoms of a cold. Several years are not cold normal, that the body’s immunity is relatively strong, the body is relatively healthy, when the pathogen invasion, the body can rely on their own immunity against pathogens. Such a physical situation should be to continue to maintain, at the same time it is recommended to go more outdoor activities to exercise, diet structure should be reasonable to ensure that adequate sleep, so that the body’s immunity will be further enhanced.