The differentiation of Exterior and Interior is not made on the basis of what caused the condition, but on the basis of the location of the disease. For example, a disease may be caused by an exterior pathogenic factor, but if this is affecting the Internal Organs, the condition will be classified as Interior.
Therefore, a disease is classified as ‘Exterior’ not because it derived from an exterior pathogenic factor but because its manifestations are such that they are located in the ‘Exterior’ of the body (the skin, muscles and channels).
There are two types of Exterior conditions: those that affect skin and muscles and are caused by an exterior pathogenic factor having an acute onset (such as an invasion of Wind Cold or Wind Heat), and those that affect the Channels and have a slower onset (such as Painful Obstruction Syndrome, also called Bi syndrome).
External diseases that begin with an invasion of an exterior pathogenic factor give rise to a typical set of symptoms and signs which are described as an ‘Exterior pattern’. It is difficult to generalize as to what these symptoms and signs are, as it depends on the other characters: that is, whether they are of the Cold or Heat pattern, and the Excess or Empty pattern.
However, generally speaking, we can say that the main symptoms of an Exterior pattern are ‘fever’, aversion to cold, aching body, a stiff neck and a Floating pulse. As a reminder ‘aversion to cold’ indicates the sudden chilliness that occurs when we fall ill with a cold or other acute exterior diseases: this is a subjective feeling of cold. ‘Fever’ (发热, Fā Rè in Chinese) does not necessarily indicate an actual fever, but rather the objective feeling of the Heat of the patient’s body on palpation.
Often the condition penetrates the upper respiratory passages including the nasal passages, the mouth and throat, the bronchioles and Lungs, as well as the skin and hair. When this occurs, all physiological aspects associated with the Lungs can be affected. Besides the upper respiratory passages, the skin, body hair and the External immune system (Wei Qi), which are all governed by the Lungs, can be damaged. The resultant acute fever, cold or flu is an attempt by the body to throw off toxins and overcome negative pathological invasions.
If the condition is one of the Cold (such as Wind-Cold) pattern, the symptoms are a slight ‘fever’, pronounced aversion to cold, severe aches in the body, severe stiff neck, no sweating, no thirst, a Floating-Tight pulse and a thin white tongue coating. The main factor to differentiate it from an Exterior-Heat pattern is the absence of thirst, the Floating-Tight pulse and the likelihood of chills (as opposed to manifest fever in Heat patterns).
If the condition is one of the Heat (such as Wind-Heat) pattern, the symptoms are fever, aversion to cold, slight sweating, thirst, a Floating-Rapid pulse, a thin white tongue coating and, sometimes, redness of the tongue on the sides and/or front. The main factor to differentiate it from an Exterior-Cold pattern is the thirst, the Floating-Rapid pulse and the predominance of fever (as opposed to chills in Cold patterns).
External Wind Cold Evil or External Wind-Heat Evil also refer to various imbalances and diseases of the upper respiratory tract including colds, influenza, rhinitis and other respiratory allergies. Rheumatic conditions are also classified as external-Damp-Wind-Cold or external Damp-Wind-Heat. Wind is a pathology that commonly accompanies Exterior conditions. External Wind can refer to the proliferation of various bacteria and viruses. The fact that the Chinese character for Wind is a small insect might perhaps suggest that they suspected the existence of external pathogens such as germs and viruses.
If a person has a tendency to Excess, the Exterior pattern will have a Excess character. The clinical manifestations of such an Exterior-Excess pattern are fever, no sweating, severe body aches, aversion to cold, a Floating-Tight pulse and a thin white tongue coating. The main factor to differentiate it from an Exterior-Empty pattern is the absence of sweating, the rapid pulse and the severe body aches.
The clinical manifestations of an Exterior-Empty pattern are slight or no fever, sweating, aversion to wind, slight body aches, a Floating-Slow pulse and a thin white tongue coating. The main factor to differentiate it from an Exterior-Excess pattern is the sweating, the slow pulse and the relatively few body aches.
The second kind of Exterior pattern that occurs when an external pathogenic factor invades the Channels in a gradual way is called Painful Obstruction Syndrome. This is characterized by obstruction to the circulation of Qi in Channels and joints by a pathogenic factor, which can be Cold, Dampness, Wind or Heat.
In obstruction from Cold, usually only one joint is affected, the pain is severe and is relieved by application of Heat. In obstruction from Wind, the pain moves from joint to joint. In obstruction from Dampness, there will be swelling of the joints, while in obstruction from Heat, the pain is severe and the joints are swollen and hot.