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Yin-Yang Exchange Syndrome refers to a condition where a man, newly recovered from an illness but not yet fully restored, contracts a disease after sexual intercourse with a woman; this is called "Yang Exchange." Symptoms include abdominal urgency and pain, with the waist and ankles radiating pain into the abdomen. Conversely, if a woman, newly recovered but not yet fully restored, contracts a disease after sexual intercourse with a man, it is called "Yin Exchange." Symptoms include heavy body, shortness of breath, swelling of the external genitalia with a sensation of pathogenic factors moving inward, severe cramping pain in the abdomen, heat rushing up to the chest, severe headache making it difficult to lift the head, and visual disturbances (seeing spots). This occurs because diseases are exchanged between men and women, hence the term Yin-Yang Exchange Syndrome.

For treating Yin Exchange resulting from Shanghan (Cold Damage), characterized by heavy body, shortness of breath, abdominal urgency, sometimes drawing spasms in the genitalia, heat rushing up to the chest, heavy head difficult to lift, visual disturbances, and stiffness/spasms in the knees and calves, the following prescription is indicated:
Burn the crotch of a woman's underwear to ash.
Grind finely. Administer one Fangcun Bi (a traditional measuring spoon) mixed with water orally. If urination becomes smooth and pain in the yin region/headache subsides, the patient will recover.

For treating Yang Exchange, which occurs when a man, after recovering from Shanghan, contracts the disease through sexual intercourse with a woman:
Take Leek roots (remove green parts, one handful, approx. 1.5 cun in diameter) and Rat feces (14 pieces, preferably those pointed at both ends).
Add one zhan (unit of volume) of water to these two ingredients, decoct until half a zhan remains, strain, and drink warm in one dose. The appearance of sticky sweat indicates efficacy; if ineffective, prepare again.

The eruption of macules/petechiae in Shanghan often results from inappropriate purgation when it was not indicated, allowing heat to enter the Stomach due to deficiency; or from failure to purge when it was indicated, causing Stomach heat to remain unvented. Both scenarios can lead to macular eruptions. The lesions resemble brocade patterns. Red ones are easier to treat, while black ones are difficult, indicating deep penetration of heat-toxin into the Stomach.

To treat macular eruptions resembling brocade patterns caused by heat-toxin in the Stomach due to missed or inappropriate purgation in Shanghan, accompanied by restlessness and delirium at severe stages; also treats Hou Bi (throat obstruction) with swelling and pain:
Xuan Shen (Scrophulariae Radix), Sheng Ma (Cimicifugae Rhizoma), Zhi Gan Cao (Prepared Glycyrrhizae Radix et Rhizoma, each 0.5 liang).
Crush into a coarse powder. Take five Qian Bi (a traditional measuring spoon) per dose, add one and a half zhan of water, decoct to seven-tenths, strain, and take warm. Wen Du (Warm Toxicity) can also cause macular eruptions.

"Bad Shanghan" (Ruined Cold Damage) refers to conditions where physicians fail to distinguish Yin and Yang, erroneously applying sweating or purging methods, leaving the disease unresolved and transforming into complex syndromes that disrupt meridians. It also includes cases where Shanghan has passed beyond its normal transmission timeline, with heat lingering in the Zang-Fu organs, symptoms changing frequently, failing to heal over time, leading to a loss of Yin-Yang balance and regular physiological laws. All such conditions are termed Bad Disease.