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Also known as Pen Xiao, also known as Ying Xiao.
Pungent, bitter, salty; extremely cold. It sweeps away excess heat in the San Jiao (Triple Burner) and intestines and stomach, and eliminates phlegm stagnation and fullness in the chest and diaphragm. Combined with Arctii Fructus (Niu Bang Zi), it treats abscess toxins in the large intestine.
Mixed with water and applied topically, it treats flame-like erysipelas (Huo Yan Dan Du). Taken warm with infant urine, it expels a dead fetus. Mixed with porcine bile and applied topically, it treats sores caused by pea toxicity. Mixed with powder of Aquarix (Chen Xiang), it breaks yang stagnation in the lower Jiao. Ground into powder and insufflated into the throat, it treats obstruction due to throat bi syndrome (Hou Bi Bu Tong) (also treats double tongue and thrush).

Pu Xiao is re-boiled and refined; when poured into a basin to solidify, those with crystalline edges on the surface are called Mang Xiao, while those with tooth-like structures are called Ma Ya Xiao. They severely deplete the true Yin of the lower Jiao and should not be used lightly.

Pungent, salty; warm. It ascends and disperses fire in the San Jiao, and eliminates phlegm in the heart and lungs. It treats pediatric convulsive fever. Mixed with human milk and applied topically, it treats sudden heat, swelling, and pain of the head and face.
Used to drop eyes affected by redness, swelling, and pain combined with Coptidis Rhizoma (Chuan Lian). By placing Mang Xiao in wind and sunlight until all moisture evaporates, leaving a light white powder like flour, it becomes Feng Hua Xiao. Those lacking genuine efficacy are strictly prohibited from use.

Pungent, sweet; cold. It removes excess heat in the stomach and sweeps away accumulated fecal matter in the intestines. It reduces swelling, breaks stagnation, eliminates phlegm accumulation, and washes eye swelling. Combined with Cinnabaris (Zhu Sha), it treats mania due to Shang Han (Cold Damage).
Mixed with infant urine, it treats painful heart conditions due to heat jue syndrome. Pu Xiao is dissolved in running long-flowing water, boiled together with Raphani Semen (Lai Fu), then decocted again with Glycyrrhizae Radix et Rhizoma (Gan Cao), placed in a clay pot over fire to remove its salty-cold nature, and collected for use. Those with stomach deficiency without excess heat are strictly prohibited from use.

Pu Xiao, Mang Xiao, and Xuan Ming Fen all unblock solid accumulations in the large intestine; using them for deficiency-type constipation causes disaster instantly. However, distinguishing between deficiency and excess is difficult to assess accurately. Injury from the Seven Emotions leads to internal stagnation, transforming into heat congestion; if it knots in the intestines and stomach, stools become hard; hardness generates fire, which blazes within the five viscera, causing various symptoms to arise suddenly. Urgent intervention to unblock stagnation is required without delay. The Classics state: "When heat dominates internally, treat with salty and cold." There is no harm in assisting nourishing tonics with Xiao and Fen to sweep away fire; how can one rigidly adhere to the concept of deficiency in internal injury, prohibiting purgatives, and thus delaying until death? If pathogenic heat injures the Yin aspect, causing dryness and constipation of the large intestine where stool cannot pass, Xiao and Fen are highly unsuitable. Instead, heavily nourish Yin to promote blood and Qi circulation, adding seeds of Cannabis Sativa (Ma Ren), Trichosanthis Fructus (Lou Ren), Armeniacae Semen (Xing Ren), or Prunus Maritima (Yu Li Ren) to facilitate passage. If due to blazing pathogenic fire, using Xiao and Rhei Radix et Rhizoma (Huang) to purge would inevitably lead to severe Yin damage and death. Therefore, deficient fire may falsely present as solid accumulation, and prolonged excess pathogens may transform into deficiency constipation. One must examine repeatedly, know precisely whether to apply or not, to avoid error.