Exterior-interior pattern differentiation refers to the categorization of patterns according to the location of the disease, in the exterior or in the interior, superficially* seated or deeply seated.

When an external pathogenic factor invades the human body, it first attacks the superficies*. At the same time, healthy qi fights against the pathogenic factor, giving rise to exterior syndrome.* If healthy qi is weak and pathogenic qi is strong, the pathogenic factor can enter the deep layer of the body from the shallow layer, or from the exterior into the interior of the body, forming interior syndrome. Interior syndrome can also arise when there is internal damage to the viscera and bowels.

Exterior pattern is a general term for patterns that occur chiefly at the early stage of external contractions affecting the exterior part of the body. They are characterized by sudden onset, aversion to cold or to wind, fever, headache, generalized pain, thin tongue coating, and floating pulse.

The patient may also have nasal congestion*, runny nose, sneezing, or even a sore throat and slight cough.

Interior pattern is a general term for patterns that indicate the existence of disease in the interior of the body such as viscera and bowels, qi and blood, or bone marrow.

The range of interior patterns is very broad and their manifestations are various; but to sum up, those that are not exterior and not half exterior and half interior pertain to interior. Their characteristics are not aversion to cold and fever. They are usually manifested by the symptoms and signs of diseases of the viscera and bowels, qi and blood, fluid and humor.

Three conditions contribute to the formation of interior patterns. First, exterior pattern changes to interior pattern. Second, external pathogen directly attacks the interior. Third, there can be internal damage, which can be caused by seven emotions, overexertion* and fatigue, improper diet, sexual overindulgence, and injury.

Half-exterior half-interior pattern is due to affliction located between the exterior and interior of the body, marked by alternate fever and chills, fullness and choking feeling in the chest and costal region, bitter taste in the mouth, dry throat, nausea and loss of appetite, and string-like pulse.*

Differentiating the interior and exterior is mainly based on if there are aversion to cold and fever existing simultaneously, if the symptoms and signs of viscera and bowels are prominent, and the different manifestation of the tongue and pulse (Table 9-1).

Differentiation	Exterior	Interior	Half Exterior Half Interior
cold and fever	fever and cold simultaneously exist	cold without fever or fever without cold	fever and chills occurs alternatively
general symptoms and signs	headache, generalized pain, stuffy nose, sneeze	palpitation, vomiting abdominal pain	fullness and choking feeling in the chest and costal region
tongue	no obvious change	there is change	no obvious change
pulse	floating	sunken
onset, severity and course	acute onset, mild and short course	gradual onset, severe and long course