The term "dou" (smallpox/variolous rash) is named based on its morphology. Obtaining the correct form indicates a favorable prognosis (Shun), while losing it indicates an unfavorable prognosis (Ni). The dou is formed by blood into a round shape due to the influence of Qi; this image corresponds to Heaven. When the dou erupts and blood follows, the dou must be complete and clean, attaching to Qi to form a halo; this represents the function of Blood; this image corresponds to Earth. When the dou erupts and Qi follows, the halo must be bright.

Regarding color: Red indicates the initial eruption of the dou; White indicates that the pathogenic toxin has not yet resolved; Yellow indicates that the toxin is about to resolve; Dry yellow indicates that the toxin has completely resolved; Grayish-white indicates blood deficiency with Qi stagnation; Black indicates toxin stagnation with dried blood; Scorched brown indicates exhaustion of Qi and Blood. If the color changes from red to white, or from white to yellow, it is a sign of life; if it changes from red to purple, or from purple to black, it is an omen of death.

When the dou are sparse, the pathogenic fire cannot overcome the Qi and Blood, allowing the Qi and Blood to naturally resolve the toxin. Occasionally, due to weak Qi and Blood invaded by Wind-Cold, or toxin sinking inward due to diarrhea, or injury by toxic drugs, recovery may be difficult to ensure. When the dou are dense, resembling connected millet grains, it indicates that Qi and Blood cannot withstand the pathogenic fire, leading to internal wind stirring, disharmony between the interior and exterior, imbalance of Ying and Wei, and blockage of the seven orifices; can such a condition be easily treated? Occasionally, those with strong Qi and Blood have dou that are round, clean, and non-confluent, with ruddy and vibrant color without stagnation; even if dense, they are treatable.

(Zhen refers to measles, Ban refers to macular rash/toxin. Zhen is smaller than dou and appears in patches; Ban is larger than dou and is red-purple.)

Dou toxin originates from the Zang organs and is deep; Zhen and Ban originate from the Fu organs and are superficial. Zhen and Dou are affected during the process of transformation and transportation, thus they are easy to resolve via the meridians. Cases that are difficult to resolve occur when there is internal excess combined with external invasion of Wind-Cold. Dou resolves from the exterior, while Zhen resolves from the interior; this is the unchanging standard method. However, at the time of dou eruption, if the toxin tends toward the hundred orifices,被封固 (sealed) by Wind-Cold closing the Couli (pores), coupled with robust Qi and Blood, steaming dampness, and blazing fire, which stirs up Fu organ toxin, resulting in simultaneous eruption of dou and zhen, these are all unfavorable signs.

If the dou are sparse, Shengma Tang (Cimicifugae Decoction) can be used to resolve them; after the zhen disperses and the dou erupts, the progression will naturally be smooth. If the dou are too excessive, although the zhen resolves, the Qi and Blood have already been depleted; one must fear that internal deficiency prevents convergence, making it difficult to predict survival. In cases with concurrent Ban (macular rash), it is due to excessive Blood and deficient Wei Qi (Defensive Qi), which fails to tightly protect the collaterals, causing excessive Blood to carry Dou toxin upward floating. This is what Chen referred to as "Sanfan Douzhen" (Three-turn Dou-Zhen). Once the dou erupts and reaches full development, the interior must be deficient; if the interior is deficient, the Ban resolves from within. If it does not resolve, use Shengma Tang modified with Dang Gui (Angelicae Sinensis Radix) and Bai Shao (Paeoniae Radix Alba) as the main prescription. There are also cases where residual toxin erupts after scabbing forms; intense heat causes internal differentiation of Ban, leading to ulceration. Treat with Jiedu Tang (Detoxification Decoction) added with Dang Gui, Bai Shao, and Fang Feng (Saposhnikoviae Radix); for severe cases, use Da Lianqiao Yin (Large Forsythia Drink) externally applied with Shengji San (Flesh-Regenerating Powder); there will be no failure to heal. If concurrent toxin erupts initially with color red like fire, it is due to toxin stagnation preventing dissemination. One should administer Sishun Qingliang Yin (Four-Obedience Cooling Clearing Drink), inducing defecation once or twice to reduce symptoms, then the Blood adheres to Qi position; urgently advance Sijunzi Tang (Four Gentlemen Decoction) added with Huang Qi (Astragali Radix), Sheng Jiang (Zingiberis Rhizoma Recens), and Da Zao (Jujubae Fructus). If diarrhea persists, add Rou Dou Kou (Myristicae Semen). Medications must be pre-decocted and administered immediately after the Ban recedes to prevent damage and sinking. The timing of medication is likened to military strategy.