Colds are short for upper respiratory tract infections, and it is normal for a normal population to have about 5 colds a year. Especially in the spring and fall seasons, when the temperature is cold and hot, it is most likely to cause the human body’s immunity to decline, and be invaded by viruses, bacteria, mycoplasma, chlamydia, rickettsiae and other pathogens, and then through the droplet transmission way to spread to the surrounding healthy people and thus cause a wide range of contagion, such as the influenza. So usually, especially in the time period and season of cold and flu to avoid cold, avoid sudden cold, hot temperatures; at the same time, you can also do physical exercise in order to enhance physical fitness, improve immunity, to ensure that there is a strong resistance to pathogens of the defense ability to reduce the frequency of cold and flu.