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The *Huangdi Neijing* (Yellow Emperor's Inner Canon) states: "All conditions of dryness, withering, contraction, stiffness, and scaling belong to Dryness." This refers to the Qi of Yangming Dry Metal, associated with the Lung and Taiyang channels, hence termed Dryness. All things are influenced by Fire; diseases caused by Dryness belong to the transformation of Dry Metal. However, while Metal is inherently dry, it is Fire that causes the body to become dry. Metal is the master of Yin and the source of Water. If affected by Dryness Qi, the source of Cold Water's generation at the upper Jiao becomes exhausted, unable to irrigate the whole body and nourish the bones and muscles. This leads to a dry complexion lacking luster, explaining why hair grows on the skin. Such conditions arise from various causes: excessive purgation after severe illness, loss of Body Fluids due to vomiting or diarrhea, misuse of mineral drugs in preventive health care, deficiency induced by sexual exhaustion, use of overly warming and drying tonics, heavy flavors in diet, excessive spicy and hot foods, consumption of strong wine, and eating roasted meats. These factors can excessively assist raging Fire, damaging True Yin. The latent Fire within Yin gradually cauterizes, depleting Blood and causing Dry-Heat to intensify, leading to various diseases. Externally, this manifests as wrinkled and scaling skin; superiorly, as scorched and dry throat and nose; centrally, as decreased fluids causing irritability and thirst; inferiorly, as withered intestines and stomach, lack of lubricating fluids, and difficult defecation; in the limbs, as flaccidity and weakness; and in the pulse, as thin, choppy, and faint qualities. All these result from Yin-Blood being damaged by Fire-Heat.

Liu Wansu in the *Yuanbing Shi* (Treatise on the Causes of Diseases) states: Wind, Fire, and Heat are Yang; Cold, Dryness, and Dampness are Yin. Yet Dryness and Dampness differ slightly. Although Dry Metal belongs to Autumn Yin, it differs from Cold-Dampness and resembles Wind-Heat. When Fire-Heat prevails and Metal declines, Wind arises. Wind overcomes Dampness, and Heat consumes fluids, potentially creating a relative cold state, resulting in Excess Yang and Deficient Yin. Thus, Wind-Heat surpasses Water-Dampness, manifesting as Dryness. Most wind diseases stem from extreme Heat generating Wind; Dryness is often a concurrent transformation, primarily driven by Heat. Due to Excess Yang and Deficient Yin, if Wind-Heat is too severe and overcomes Water-Dampness, Dryness forms. The Liver governs the Tendons. If Wind is excessive and compounded by Dry-Heat, fluids gather in the chest and diaphragm rather than nourishing the extremities, causing the tendons to become overly dry. Dry Metal governs contraction and firmness; Kidney Qi becomes stagnant, leading to stiff and tense tendons, urgency, and lockjaw. Alternatively, extreme Dry-Heat may cause the Spleen and Stomach to become withered, resulting in Xiao Ke (Wasting-Thirst Syndrome). Or, if Wind-Heat-Dryness is severe and stagnates in the exterior, while interior Qi is balanced, symptoms include frequent stretching and yawning, tendon spasms, occasional aversion to cold, muscle twitching and convulsions, with a floating, rapid, and wiry pulse. If Wind-Heat-Dryness stagnates deeply in the interior, it causes irritability, fullness, and constipation. Epileptic seizures occur when extreme Heat generates Wind-Dryness as a concurrent transformation; saliva overflows into the chest and diaphragm, Dry-Heat cauterizes causing convulsions, and consciousness is lost with rigid collapse. All these syndromes arise from extreme Heat. Variations between Wind and Dryness depend on the differing degrees of severity among Wind, Heat, and Dryness. Stroke causing flaccid tendons occurs because Wind-Heat overcomes Dampness to create Dryness, representing severe Dryness. Flaccid tendons failing to retract lead to Wei Bi (Flaccidity and Obstruction Syndromes); thus, various stagnation-induced flaccidity syndromes belong to Lung Metal, reflecting Dryness transformation. Just as in late autumn, severe Dryness causes plants to wither and fall without retaining leaves, mirroring disease pathology. Hence, hands grasp only when nourished by Blood, and feet walk only when nourished by Blood.

Diseases of Dryness stem from depleted Blood and unsmoothed Qi and Blood circulation. Therefore, treatment should employ Sweet-Cold and moistening agents, as both Sweet and Cold properties generate Blood. Cold overcomes Heat; when Yin is nourished, Fire subsides; when fluids are moistened, Dryness is removed. The source descends, and Essence-Blood ascends to nourish. Consequently, Qi and fluids circulate freely, internal spirit flourishes, and external luster appears. The *Neijing* principle "Dryness should be moistened" implies nourishing Blood and moistening Dryness. Some mistakenly attribute Dryness to Wind-Heat, using Pungent-Cool wind-dispelling or Bitter-Draining formulas, which further dry the fluids and cause additional damage. They fail to realize that Blood deficiency leading to Dryness often attracts Wind manifestations, due to Wood-Fire insulting the deficiency of Metal-Water. For Wind-Dryness diseases, one must seek the root cause, ensuring the treatment principle remains correct.