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Traditional Chinese medicine (TCM) has the theory that "the lung is related to the skin and body hair." Ancient medical practitioners discovered that there are numerous physiological connections between the lung and the skin and hair. For example, the most direct evidence is that exposure to wind-cold can cause coughing. Suwen-Ke Lun states: "The skin and hair are associated with the lung. When the skin and hair are first affected by pathogenic qi, the pathogenic qi follows this association."

Physiologically, both the lung and the skin can regulate body temperature through evaporation. The lung can expel water vapor, and the skin can also expel water vapor and sweat. ⁽¹⁾ If the skin loses its heat-dissipating function or body temperature rises, the lungs will compensate by increasing respiration to accelerate heat expulsion. Some animals, such as dogs, lack sweat glands and rely on panting to compensate for the inability to sweat and dissipate heat.

Human skin also has some respiratory function, and amphibians can rely heavily on their skin for respiration. There have even been discoveries of certain frog species that lack lungs and rely solely on skin respiration.

In contrast to the skin's sweating and heat dissipation, in wild animals, "fur" can also provide insulation, but this function has degenerated in humans.

TCM further believes that the vitality of the skin and hair is determined by the strength of lung qi (i.e., lung function). As Suwen-Jingmai Bie Lun states: "The lung connects with all vessels and transports essence to the skin and hair." Suwen-Wei Lun: "When lung heat causes the lobes to dry, the skin and hair become weak and thin." Lingshu-Jingmai: "When the hand Taiyin (i.e., the lung meridian, see What Exactly are Meridians and Acupoints?) qi is exhausted, the skin and hair become dry. Taiyin warms the skin and hair with moving qi, so if the qi is not nourished, the skin and hair will dry." This means that the skin and hair rely on lung qi for nourishment. If lung function is abnormal, it manifests as weak, dry skin and hair. Clinically, many skin allergies and skin diseases often co-occur with lung system disorders such as bronchitis, asthma, and nasal allergies. Many lung-treating Chinese medicinals can also treat skin diseases.

In the Five Phases classification, the lung belongs to "metal," and "metal can generate water." The skin, which is coupled with the lung, can also generate "water." Suwen-Wuyunxing Da Lun states: "The lung promotes the skin and body hair, the skin and hair generate the kidney, and the lung governs the nose." The statement "the skin and hair generate the kidney" is puzzling, but modern physiology reveals that the sweat glands of the skin, both in structure and function, resemble a miniature version of the renal glomerulus (Figure 1). The composition of sweat is very similar to that of urine. Therefore, the author believes that the sweat glands in the skin are like a second set of kidneys in the human body. Many lung-treating Chinese medicinals can also induce sweating and diuresis (such as Ephedra), which is related to this.

In the classification of the three yin and three yang in TCM, the lung belongs to Taiyin. Its meridian is the Hand Taiyin, with the hand corresponding to "heaven" (the foot corresponds to "earth"). The Hand Taiyin corresponds to the "moon" in the sky. The Shuowen (《說文》) states: "The moon is the essence of Taiyin." Therefore, the lung is also related to the moon. These attributes of the lung can explain many anatomical "coincidences." For example, anatomically, the lung is located above the diaphragm and is filled with air. In the microcosm of the human body cavity, the diaphragm symbolizes the ground, and the lung symbolizes the sky. The 12 thoracic vertebrae and 24 ribs surrounding the lung correspond to the 12 months of the year and the 24 solar terms of climate change. The segmented changes in the sky's climate correspond to the structure of the "sky" in the human body—the tissues surrounding the lung (see The Indispensable "Holographic Law" of the Human Body).

Moreover, from an anatomical perspective, the skin and hair, along with the lungs, are the two organs that most frequently come into contact with the external air. Particularly, the skin is rich in sensory receptors that can detect changes in the external air such as temperature, humidity, and other variations, and relay this external information back to the body for physiological regulation and adaptation. Suwen-Linglan Midian Lun states: "The lungs are the officials of the prime minister, from whom governance and regulation emerge." General interpretations of "governance and regulation" are often vague or overly abstract, especially the meaning of "regulation." The author believes that the "lungs" here refer to the broad "lung system," which includes the lung organ, the upper respiratory tract, and the skin and hair. The "lung system" can sense changes in external climate ("seasonal" changes) and provide immediate feedback and regulation of the body's internal physiological functions to adapt to the external environment, much like a prime minister assisting the heart in governing the body. This is the meaning of "governance and regulation."

From the above, it is clear that the lungs and skin are closely connected. Based on this understanding, we consider the lungs when treating various skin disorders or certain physiological dysfunctions. Modern medicine has yet to discover these connections and primarily views the lungs as "the respiratory organ of the body," a superficial understanding. It is no wonder that treating various skin diseases often only addresses the symptoms, with a high likelihood of recurrence after stopping medication.

bubble_chart Footnote

1. "General Physiology": The total daily water excretion of the human body is approximately 2300cc, with the lungs accounting for 350cc, the skin for 350cc, sweat for 100cc, and urine for 1400cc. These figures are based on conditions without excessive water intake or exercise. The lungs and skin account for one-third of the total water excretion, highlighting the importance of the "lung system" in water regulation.