During the course of disease and under certain conditions, there may appear simultaneous internal and external disorder, transmission of pathogenic factors from the exterior into the interior and from the interior to the exterior.

Simultaneous external and internal disorder:
At the same stage, there appear both external syndrome and internal syndrome. The causes of such a morbid condition are various. It may be caused by invasion of pathogenic factors into both the external and internal phases marked by appearance of both external syndrome and internal syndrome at the early stage, or by transmission of pathogenic factors into the interior when the external syndrome is not cured yet, or by contraction of new disease when old one is not cured yet, such as internal impairment followed by contraction of exogenous disease or contraction of exogenous disease followed by improper diet, etc.

Simultaneous appearance of both external and internal syndromes often appears together with cold and heat as well as asthenia and sthenia, usually manifesting as external heat and internal cold, external cold and internal heat as well as external sthenia and internal asthenia, etc. which will be discussed in the following sections.

External and internal transmission:
During the course of disease and under certain conditions, external pathogenic factors fail to be relieved and transmit into the interior, bringing about internal syndrome; in some internal syndromes, pathogenic factors transmit from the interior to the exterior and produce some external symptoms.

Transmission of exterior pathogenic factors into the interior:
Internal syndrome appears after external syndrome and external syndrome disappears with the appearance of the internal syndrome. Such a morbid condition is caused by hyperactivity of pathogenic factors, or by frequent deficiency of healthy qi, or by improper nursing, or by delayed or erroneous treatment that reduces resistance of the body and leads to transmission of pathogenic factors from the external to the internal. This morbid condition is usually seen in the course of exogenous diseases.

For example, external syndrome manifests such symptoms like aversion to cold, fever, headache and body pain, whitish thin fur and floating pulse, etc. Transmission of exterior pathogenic factors into the interior and external syndrome transforming into internal syndrome can be distinguished by such changes like disappearance of aversion to cold and aversion to heat together with high fever, thirst with desire to drink, reddish tongue with yellowish fur and fast pulse, etc.

Transmission of pathogenic factors from the interior to the exterior:
Under certain conditions in some internal syndromes, pathogenic factors transmit from the interior to the exterior, leading to the appearance of some external symptoms and alleviation of the internal syndrome. This is the result of proper treatment and nursing that have strengthened the resistance of the body and driven pathogenic factors out of the body. For example, high fever, restlessness, chest oppression, cough and dyspnea in primary disease followed by disappearance of fever after sweating, or eruption of measles and milliaria alba as well as alleviation of restlessness, chest oppression, cough and dyspnea is the sign of pathogenic factors transmitting from the internal to the external.

Transmission of pathogenic factors from the exterior to the interior is a sign of aggravation of pathological changes, while transmission of pathogenic factors from the interior to the exterior signifies the decline of disease. Cognition of such changes is significant for judging the development and changes of diseases.