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Cough (Ke) refers to a condition with sound but no phlegm, indicating injury to the Lung Qi resulting in unclear voice; Su refers to a condition with phlegm but no sound, caused by Spleen dampness stirring up phlegm qi. Cough and Su together refer to having both phlegm and sound, resulting from external pathogens damaging the Lung tissue, which subsequently stirs up Spleen dampness. However, the manifestation of phlegm lies in the Spleen, while its root lies in the Kidney. Therefore, some cases are suitable for treatment with drying agents to eliminate phlegm, while others require moistening agents to resolve it. In children, this is mostly caused by Wind-Cold or milk/food stagnation, and should be treated with drying methods to eliminate phlegm and acrid methods to disperse it, using herbs such as Banxia (Pinelliae Rhizoma), Chenpi (Citri Reticulatae Pericarpium), and Qianhu (Peucedani Radix). Although the *Classic* states that all five Zang and six Fu organs can cause cough, they must each receive their respective pathogens, yet ultimately cannot depart from the influence of the Lung. When Su is caused by phlegm, phlegm is the primary issue, and treatment focuses on the Spleen; when Cough is triggered by phlegm, Cough is the primary issue, and treatment focuses on the Lung.

From the perspective of seasons: Cough in Spring is due to the rising of Spring Qi; Cough in Summer is due to the flaming upward of Fire Qi; Cough in Autumn is due to Damp-Heat injuring the Lung; Cough in Winter is due to external contraction of Wind-Cold.

From the perspective of a 24-hour cycle: Cough in the early morning belongs to Phlegm-Fire; Su in the late morning belongs to Stomach Fire; Su in the afternoon belongs to Yin Deficiency; Su at dusk indicates Fire Qi floating in the Lung Meridian; Su at Wugeng (3–5 AM) indicates food stagnation in the San Jiao.

Cough due to Lung Excess must present with paroxysmal coughing while holding the head, red face, and desire to eat despite illness; Cough due to Lung Deficiency must present with rebellious Qi and empty wheezing, pale complexion, and undigested stool diarrhea; Cough due to Lung Heat must present with fishy-smelling and thick phlegm, fever, panting, chest fullness, dry nose, red face, and rubbing of the eyebrows, eyes, nose, and face; Cough due to Lung Cold must present with frequent coughing, thin phlegm, pale face, panting, gooseflesh skin, borborygmus, aversion to wind, and excessive sweating.

However, although Su primarily concerns the Lung, it actually originates from the Heart. If Heart Qi is excessive, Fire will scorch Metal (Lung), and treatment should suppress the Heart and nourish the Lung. If Spleen Qi is deficient and cold, it fails to generate support for the Lung, leading to insufficient Lung Qi, external invasion of Wind Pathogens, and internal generation of Phlegm-Dampness; treatment should tonify the Spleen and Lung. If Spleen Excess causes middle jiao blockage and steaming heat rises upward, treatment should drain the Spleen and clear the Lung. Thus, Heart overacting on Lung is considered "Thief Evil," Liver overacting on Lung is "Minor Evil," Kidney overacting on Lung is "Solid Evil," Spleen overacting on Lung is "Deficient Evil," and Lung self-disease is "Correct Evil." Those who expel phlegm immediately upon one cough have Spleen Deficiency unable to control dampness, resulting in slippery phlegm; those who cough continuously for ten-plus times without expelling phlegm have Lung Dryness overcoming Phlegm-Dampness. For slippery phlegm, use Arisaemae Rhizoma (Nanxing) and Pinelliae Rhizoma (Banxia) to dry the Spleen; at this time, Qi-moving agents should be avoided. For dry/sticky phlegm, use Aurantii Fructus (Zhike), Perillae Fructus (Suzi), and Armeniacae Semen Amarum (Xingren) to benefit the Lung; at this time, Spleen-drying agents should be avoided.

Generally, if Spleen Qi is insufficient, it cannot generate Lung Qi, making one susceptible to Wind Pathogens; thus, cases of Lung Cold are all due to Spleen Deficiency. Cases of Lung Heat are mostly due to Spleen Excess. If symptoms include retracted lips, sunken chest, saw-like sounds in the throat, dry and scorched-black nose, rough coughing breath, and abdominal distension and pain, it is a death prognosis. If chronic cough leads to hoarseness, staring eyes, hand pulling/twitching, crow-like vocalization, abdominal distension, rapid panting, and frequent fright, it will inevitably transform into a Wind syndrome and result in death. If there is hoarseness like a saw, cyanosis of lips and face, depression below the neck, saliva as sticky as glue, foul odor in the mouth, severe panting with retracted lips, it is also a death prognosis. As for cough occurring within the first hundred days of life, named "Milk Cough" (Ru Sou), the Lung leaves are particularly delicate and easily injured, requiring urgent treatment. If delayed, blood vessels will penetrate the face, causing purple-black circles around the eyes, or the whites of the eyes turning red like blood, called "Blood Eyes." At this point, use Shengdi Huang (Rehmanniae Radix) and Heidou (Phaseoli Semen Nigrum), ground together into a paste, applied over the eyes, so that the dark circles will naturally disappear, and the blood will exit with tears, leading to recovery.