In Western medicine, a cold may be caused by bacteria and viruses such as rhinoviruses, while the flu is the result of being infected with influenza viruses. Traditional Chinese medicine (TCM), instead of a microscopic understanding, uses a macroscopic and holistic concept to explain the phenomena of cold and flu. They are considered illnesses caused by unfavorable influences in the climatic and seasonal environments in nature, which are classified under exogenous evil qi.

Seasonal changes in nature are believed to have considerable influences on the human body. If the human body is weak, pathological factors will take the opportunity to attack the body, leading to cold and flu. The unfavorable influence of the seasonal changes is perceived as an evil that threatens our health. The concept of bacteria and viruses causing illness are incorporated in the concept of exogenous evil qi in Chinese medicine, but it is classified with different diagnosis and treatment systems.

Under the category exogenous evil qi, there are six evils, namely "wind evil" (a wood element/ more prevalent in spring), "summer heat evil" (a fire element/more prevalent in summer), "fire evil" (a fire element more prevalent in summer), dampness evil (an earth element more prevalent in late summer), dryness evil (a metal element more prevalent in autumn) and "cold evil" (a water element more prevalent in winter). Among them, the wind evil is considered the leading evil qi that most frequently causes cold and flu. But evil qi seldom attacks alone, it is usually accompanied by some other evil qi depending on the seasonal influence. For example, wind-cold evils are more prevalent in winter while wind-heat evils are more prevalent in spring and summer.

TCM treatment for cold and flu does not focus on direct removal of virus or bacteria on a microscopic level. Instead, it focuses on resuming the internal harmony of the human body. From a Western viewpoint this might be explained as modifying the internal environment of the human body, so that the virus or bacteria can no longer find a good habitat or environment in the human body to survive. By resuming the healthy internal ecology inside human body, the symptoms of cold and flu will gradually go away and the illness will then be treated.

In Chinese medicine understanding, symptoms of cold and flu are the result of a battle between the protective qi of the body and the invading exogenous evil qi. Protective qi is a kind of vital energy responsible for protecting the body against the influences of the exogenous evil qi. It circulates around the whole body through the skin and muscles located in the "exterior" to guard against the attack of the evil qi.

A certain degree of a fear of cold is the first sign of cold and flu. It is an indication that the evil qi is attacking the human body. Being warm in property, when protective qi fights fiercely against the evil qi, it will lead to a rise in body temperature and the development of a fever. Therefore, the higher the fever, the fiercer the fight between the two forces and hence the more severe the cold and flu is. The degree of fever and fear of cold helps differentiate what kind of evil qi is invading.