Among the classical prescriptions for Lung Heat, Xie Bai San (Drain the White Powder) stands apart from the bitter-cold formulas that dominate this category. Where Huang Qin, Huang Lian, and similar herbs attack Lung Fire directly through bitter-cold suppression, Xie Bai San achieves the same outcome through a gentler mechanism — sweet-cold clearing combined with Yin nourishment. Created by the Northern Song paediatric physician Qian Yi (Qian Zhongyang) for children whose constitutionally delicate Yin cannot tolerate harsh cold, this four-herb prescription has since proven applicable to adults wherever Lung Heat presents with Yin insufficiency or constitutional fragility. For nearly a thousand years it has remained the standard formula for what TCM identifies as Lung Heat wheezing-cough: persistent dry cough, scanty phlegm, skin that feels warm to the touch (especially at the surface), and afternoon fever — the pattern the Xiao Er Yao Zheng Zhi Jue described as “Lung excess with urgent Qi and wheezing-cough.”

I. Historical Background

Xie Bai San is recorded in Qian Yi's Xiao Er Yao Zheng Zhi Jue (Key to Syndrome Identification and Treatment in Paediatrics), China's earliest surviving paediatric monograph. Originally named Xie Fei San (Drain the Lung Powder), it was renamed after the Lung's Metal correspondence (Metal = white colour) — hence Xie Bai (Drain the White). Qian Yi formulated it specifically for children's constitutionally “delicate Yin,” recognising that the bitter-cold approach would damage their immature Spleen-Stomach.

Subsequent medical commentaries consistently praised its refinement. Qing Dynasty physician Wang Ang (Yi Fang Ji Jie) called it “the standard for all Lung-draining formulas.” Wang Zijie (Jiang Xue Yuan Gu Fang Xuan Zhu) emphasised its quality of “draining without damaging the delicate organ.” The formula’s scope expanded progressively from paediatrics to adult respiratory and dermatological medicine, wherever Lung-Fire patterns present with Yin insufficiency.

II. Four-Herb Composition and Formula Analysis

Classic composition (reference Xiao Er Yao Zheng Zhi Jue; modern clinical doses):

• Sang Bai Pi (dry-fried) 15g, Di Gu Pi 15g, Zhi Gan Cao 3g, Jing Mi (round-grain rice) 6g (one handful)

Traditional preparation: grind all four ingredients into coarse powder; add one handful of Jing Mi, decoct together until rice is seven-tenths cooked; strain and take warm before meals. Modern practice: water decoction, once daily in 2 doses; adjust for age and constitution.

Chief herb — Sang Bai Pi (dry-fried Mulberry root bark): sweet, cold; enters Lung. Core action: drains Lung Heat, stops cough and calms wheezing, promotes urination. Why dry-fried? Raw Sang Bai Pi is cold and can irritate the Spleen-Stomach; dry-frying (chao) moderates its cold nature, making it more appropriate for prolonged use and paediatric patients without losing its Heat-clearing efficacy. Modern pharmacological research confirms Sang Bai Pi contains sangigenol, sangicoside, and related compounds with measurable antitussive, expectorant, bronchodilatory, anti-inflammatory, and antipyretic effects. Its mild diuretic action assists in expelling Heat-pathogens through the urine. The Lung is the “delicate organ” (娇脏) that prefers moistening and dislikes dryness; Sang Bai Pi’s sweet-cold-moist nature respects this physiology, clearing Heat without the drying damage of bitter-cold herbs.

Deputy herb — Di Gu Pi (Wolfberry root bark): sweet-bland, cold; enters Lung, Liver, Kidney. Core action: clears and vents hidden Fire (fu huo) from the Lung and Blood division, nourishes Yin and retreats deficiency-Heat. The critical distinction from Sang Bai Pi: Sang Bai Pi drains manifest Lung Heat (easily recognisable, causing cough and wheezing); Di Gu Pi clears hidden Fire — Heat lurking in the Lung that is less obvious but causes the characteristic afternoon fever and skin surface warmth. The combination of one herb clearing manifest Heat and one clearing hidden Fire is the formula’s diagnostic signature. Wang Ang (Yi Fang Ji Jie): "Sang Bai Pi is sweet and supplements the insufficiency of primordial Qi, pungent and drains the surplus of Lung Qi, eliminates phlegm and stops cough; Di Gu Pi is cold and drains the hidden Fire of the Lung, bland and drains the deficiency-Heat of Liver and Kidney, cools the Blood and retreats steaming."

Assistant and envoy — Zhi Gan Cao and Jing Mi: both sweet and neutral; enter Spleen, Stomach, Lung. These two herbs are the formula’s Spleen-Stomach guardians and Lung-Yin supplementors:

• Zhi Gan Cao: supplements Qi and warms the Middle; harmonises Sang Bai Pi and Di Gu Pi’s cold nature; prevents cold-natured herbs from damaging the Spleen-Stomach; additionally, the TCM principle “Spleen is the Mother of the Lung” — strengthening the Spleen-Stomach reinforces the Lung’s inherent Qi (pei tu sheng jin — “cultivating Earth to generate Metal”).
• Jing Mi (round-grain white rice): supplements Middle Jiao Qi, harmonises the Stomach, nourishes Lung Yin, moistens and clears, relieves thirst and restlessness. Jing Mi’s moistening nature additionally soothes Lung-Yin dryness from Heat damage. Practically, it also improves palatability — an important consideration in paediatric medicine. The combination of Zhi Gan Cao and Jing Mi embodies the formula’s “clear and supplement, drain and reinforce” design principle.

Formula architecture — three characteristics:
① Clear while moistening (qing zhong you run): Sang Bai Pi and Di Gu Pi clear Lung Heat; their sweet-cold-moist nature simultaneously nourishes Lung Yin rather than drying it further
② Drain while supplementing (xie zhong you bu): the two chief herbs drain Lung Heat; Zhi Gan Cao and Jing Mi supplement Spleen-Stomach and nourish Lung Qi — supplementing the substrate while draining the pathogen
③ Gentle without injuring righteous Qi (ping he bu shang zheng): no bitter-cold harsh drugs; the formula’s sweet-cold-bland character is safe for children, the elderly, and constitutionally weak patients during sustained use

III. Pattern Identification and Clinical Applications

Core pattern: Lung hidden Heat (Lung smouldering Fire)
Persistent dry cough with scanty sputum, or wheezing with shortness of breath; skin feels warm or hot to the touch (especially the surface); afternoon or late-day low-grade fever; mouth and throat dryness; tongue red with thin yellow coating; thin rapid pulse. The skin warmth is diagnostically significant — the Lung governs skin and body hair, and Lung Heat vents outward through the skin surface.

Modern applications:

• Paediatric: persistent dry cough after upper respiratory infection; childhood bronchitis (Heat type); paediatric asthma during non-acute periods (Lung-Heat type). Children with “persistent cough after cold” — fever cleared but cough continues, scanty sticky sputum, red tongue — fit the pattern well. Case example: 6-year-old girl, persistent cough 2 weeks post-cold, dry cough with slight wheezing, scanty yellow sputum, skin warm to touch, afternoon fever, tongue red with thin yellow coating, rapid pulse. Xie Bai San plus Xing Ren 9g, Zhe Bei Mu 9g, Pi Pa Ye 9g (wrapped). After 5 doses: cough and wheezing markedly reduced, fever cleared, sputum absent; 3 further doses: full resolution.
• Adult respiratory: chronic bronchitis and COPD with Lung-Heat pattern; pneumonia recovery phase with residual dry cough and low-grade fever; post-COVID respiratory sequelae with dry cough and skin surface warmth.
• Skin conditions: Lung governs skin and body hair — Lung-Fire patterns can produce eczema, acne, or urticaria with skin warmth and redness. Xie Bai San with appropriate additions addresses the Lung-Heat driving surface manifestations.

Common clinical modifications:

• Lung Heat severe (cough with yellow sticky sputum, thirst): add Huang Qin 9g, Zhi Mu 9g
• Yin deficiency (dry mouth, hot palms, night sweats): add Mai Dong 12g, Sha Shen 12g, Bai He 12g
• Cough with scanty yellow sputum difficult to expectorate: add Zhe Bei Mu 9g, Pi Pa Ye 9g, Gua Lou 12g
• Wheezing prominent: add Xing Ren 9g, Su Zi 9g
• Blood-tinged sputum (Lung Heat injuring Blood vessels): add Bai Mao Gen 15g, Ce Bai Ye 12g
• Paediatric Lung-excess wheezing (original indication from Xiao Er Yao Zheng Zhi Jue): combine with Bu Fei E Jiao San for concurrent Yin deficiency

IV. Usage, Dosage, and Safety

Patent forms: Hai Tian Xie Bai San granules and Nong Ben Fang Xie Bai San. Decoction: take warm before meals. Paediatric dose: reduce proportionally by age and weight.

Contraindications:

• Spleen-Stomach Cold deficiency (cold aversion, abdominal distension, loose stools, pale tongue, white coating): Sang Bai Pi and Di Gu Pi’s cold nature will worsen Cold-deficiency symptoms; use under guidance with dose reduction and warming additions
• Cold-type cough (clear thin white sputum, no thirst, cold aversion, pale tongue): this pattern is the opposite of the formula’s target; using Xie Bai San will worsen it
• Pregnant women: Di Gu Pi has mild Blood-cooling action; use under supervision
• Allergy to any component: contraindicated

Dietary and lifestyle support during treatment: foods that nourish Lung Yin and clear Lung Heat: snow pear, silver ear (Tremella), lily bulb (Bai He), water chestnut (Bi Qi), lotus root, winter melon; avoid spicy, oily, hot-natured foods (chilli, Sichuan pepper, lamb, deep-fried); avoid smoking and smoke exposure; maintain adequate hydration (2000ml daily); rest, moderate exercise; avoid over-exertion and late nights (which deplete Yin); keep indoor humidity adequate.

Xie Bai San’s clinical longevity reflects a genuine therapeutic insight: the Lung is the “delicate organ” that tolerates neither bitter-cold assault nor cloying supplementation. A formula that clears its Fire through sweet-cold moistening, supports its function by strengthening its Spleen-Stomach mother, and does so without harsh herbs, can be used safely across age groups and for sustained durations. The formula is pattern-specific — Lung smouldering Heat with Yin-insufficient substrate is its precise target; Cold-type or Qi-deficiency respiratory patterns require entirely different approaches.