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Yi Bing (Disease of Exchange) refers to the transmission of pathogenic factors through the interaction of Yin and Yang. It typically occurs when a patient has just recovered from a severe illness, but residual pathogens remain in the body. If sexual intercourse is engaged in under these conditions, toxic qi returns and becomes obstructed, leading to mutual infection. If a male patient, newly recovered, contracts the disease after intercourse with a female, it is called "Yang Yi" (Yang Exchange). If a female patient, newly recovered, contracts the disease after intercourse with a male, it is called "Yin Yi" (Yin Exchange). If the disease recurs or worsens without such contact, it is termed "Nü Lao Fu" (Female Exhaustion Recurrence), which is generally treated with modified Xiaoyao San (Free and Easy Wanderer Powder). In males, symptoms include swelling of the genitals and colicky pain in the lower abdomen. In females, symptoms include abdominal urgency, heaviness in the waist and hips, and pulling pain extending into the abdomen. Clinical manifestations involve heat rushing up to the chest and heart, shortness of breath, heavy body, inability to lift the head, immobility of the feet, visual disturbances ("seeing flowers"), spasticity of the four limbs, laxity of all joints, retraction of the testes into the abdomen in males, and pain radiating to the vagina in females. These are treated with Shao Kun San (Burnt Underwear Powder), or formulas containing Jia Shu Fen (Ass's Dung) or Zhu Pi San (Bamboo Rind Powder). Recovery is indicated by the free passage of urine and the subsidence of swelling at the glans penis. However, if there is curling of the hands and feet, protrusion of the tongue, and a pulse that deviates from the normal course (Li Jing Mai), it is considered an incurable condition.

Fa Yi (Swollen Cheek/Jaw) occurs when sweating in Shang Han (Cold Damage) is incomplete, causing pathogenic factors to knot in the area one cun and two fen behind the ear, or causing hardness and swelling below both ears. This results from residual heat and toxins not being cleared. Prompt dispersal is required; otherwise, swelling will lead to suppuration. Lian Qiao Bai Du San (Forsythia Decoction for Resolving Toxins) is appropriate.

When Yang Qi declines in the lower part of the body, it results in Cold Jue (Reversal Cold). When Yin Qi declines in the lower part, it results in Heat Jue (Reversal Heat). The Classics state: Yang Qi originates from the lateral aspect of the five toes, and Yang meridians converge at the sole and gather at the center of the foot; thus, excess Yang leads to heat in the soles. Yin Qi originates from the medial aspect of the five toes, and Yin meridians converge below the knees and gather at the center of the foot; thus, excess Yin leads to coldness from the five toes up to the knees. In other cases, such as Shang Han or epidemic diseases, where extreme heat penetrates deeply causing cold hands and feet, this is known as "the deeper the heat, the deeper the Jue," representing "extreme Yang resembling Yin." Misdiagnosing this as cold and administering hot medicines can cause death instantly. Cheng Qi Tang (Pulse-Regulating Decoction), Bai Hu Tang (White Tiger Decoction), and Da Chai Hu Tang (Major Bupleurum Decoction) are suitable. For true Yin-cold Jue, warming Yang formulas like Fuzi Lizhong Wan (Aconite and Ginger Pill for Regulating the Middle) are indicated. For Heat Jue due to Yin deficiency, nourishing Yin to control fire is appropriate. Additionally, when Fire is constrained within the Spleen Earth, causing extreme heat in the hands and feet, this is the rationale for Li Dongyuan's creation of Sheng Yang San Huo Tang (Raising Yang and Dispersing Fire Decoction).