Lung governs the skin and body hair

The skin and body hair are closely related to lung function. Plain Questions (素问 sù wèn, yīn yáng yìng xiàng lùn) states, The lung engenders the skin and body hair, which is explained as meaning that the skin and body hair are dependent on the essential qì supplied by the lung. Certain forms of lung vacuity such as lung wilting may be reflected in dry lusterless skin.

In a broader sense, the skin and body hair represent the exterior of the body as a defense against external evils. Invasion of external evils is associated with disturbance of normal sweating (absence of sweating or profuse sweating). The function of resisting evils and controlling perspiration is also related to the supply of defense qì. The Magic Pivot (灵枢 líng shū) states, Defense qì warms the flesh and flushes the skin; it replenishes the interstices and controls their opening and closing. Its capacity to fulfill these functions is mainly attributable to the diffusion—or gentle outward movement—of lung qì. This is discussed in The Magic Pivot (灵枢 líng shū) in the following way: The upper burner opens, diffuses the five flavors [i.e., foods of the five flavors], nourishes the skin, fills the body, and moistens the hair, just as the dew waters the earth. The sweat pores, referred to in Plain Questions (素问 sù wèn, shēn qì tōng tiān lùn) as qì gates were believed to have the function of diffusing lung qì.

The relationship of the skin and body hair to the lung can be seen in disease. Although the lung itself is in the interior, its governing the qì of the whole body and its intimate relationship with defense qì in particular place it on the first line of the body’s defense’s to external evils. External evils assailing the fleshy exterior usually cause lung disease such as sore throat and nasal congestion. When lung qì is vacuous, the fleshy exterior become insecure, allowing sweat to flow out (spontaneous sweating).

NB: The lung is the only viscus to be affected by invasion of external evils manifesting in exterior patterns.

Etymology

Chin 皮 pí, skin, integument; 毛 máo, hair, or specifically hair of the body as opposed to that of the head.