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Pain is generally considered excess (Shi, 实), while itching is generally considered deficiency (Xu, 虚). Excess refers to the abundance of pathogenic factors; deficiency refers to the weakness of healthy Qi. Sores and rashes are caused by Fire. When Fire is vigorous, pain occurs; when Fire is mild, itching occurs. Therefore, constant pain indicates an excess of pathogenic factors. The toxicity of smallpox erupts between the skin, hair follicles, muscles, and flesh. It is constrained by Qi and moistened by Blood, fermenting its toxicity until transformation. If Healthy Qi is complete and unrelenting, and the toxic vapors have transformed but not yet fully formed, stagnation leads to pain; this is the normal state. When the toxicity transforms into pus and takes shape, the pain ceases on its own. However, severe pain resembling knife cuts or needle pricks, accompanied by loud crying and wailing, indicates damage to the skin and flesh, meaning the body cannot withstand the toxicity. This is a variation of pain, representing a "bad syndrome" (Huai Zheng, 坏症) with poor prognosis. Constant itching indicates deficiency of Healthy Qi. The *Classic* states: "The Stomach is the sea of water and grain, the great source of the six Fu organs." Flavors enter the mouth and are stored in the Stomach to nourish the five Zang organs. If Stomach Qi is deficient, water and grain fail to transform, internal fluids dry up, and essence cannot be transported to the skin and hair. Qi loses its defensive function, and Blood loses its nourishing function, failing to ferment toxic vapors into formation. Consequently, toxic vapors float, sink, hide, and vanish suddenly, burning the skin and hair, causing itching. Treatment should tonify Qi and Blood, harmonize the middle, and support the interior to expel toxins; the itching will then cease. If itching persists, leading to scratching that destroys the skin and leaves muscle pits, this indicates internal sinking of toxic vapors and external collapse of Healthy Qi, leading to death shortly thereafter.

However, pain preceding itching is a normal pattern. Initially, the toxin has not resolved or transformed, and Fire is vigorous, causing pain. Later, pus forms, the toxin resolves, and Fire energy gradually diminishes, causing itching. Nevertheless, neither pain nor itching should be excessive. The *Classic* states: "All pain, itching, sores, and ulcers belong to Heart Fire." Vigorous Fire causes blood heat; heat causes dryness; dryness causes Qi stagnation, resulting in pain. Pain upon initial eruption indicates that the pathogen has not been fully dispersed, and heat-toxicity is scorching the skin and muscles. Dense eruptions accompanied by pain indicate abundant toxicity and blood stasis. Before the sixth day, dispersing methods are mostly used; after the sixth day, blood-invigorating methods are mostly used. For pain due to dryness and stagnation, bathing with Shuoyang Decoction (Water Willow Decoction) is appropriate. Regarding smallpox itching: if the patient can eat and has hard stools, it indicates internal excess of pathogenic factors and external deficiency of Healthy Qi. If the patient is fatigued, lacks appetite, and has diarrhea, it indicates internal deficiency of Healthy Qi and external excess of pathogenic factors. Additionally, Fire pathogens combusting between the skin and muscles, unable to emerge immediately, cause dryness and burning of the interstices (Cou Li, 腠理), leading to itching. There are also cases where drunk individuals approach heat sources, or wear heavy clothing/bedding, causing itching. Furthermore, when Blood is circulating freely but is bound externally by Wind-Cold, stagnation leads to itching. Generally, if the smallpox color is purple-red, the patient can eat, and Qi and Blood are sufficient, the itching belongs to Blood Heat; treatment should focus on clearing heat and detoxifying. If the color is not red and vibrant, the patient refuses milk/food, and Qi and Blood are insufficient, the itching belongs to Deficiency-Cold. Since the Stomach governs muscles and is the source of Qi and Blood, treatment should regulate the Spleen, promote appetite, invigorate Blood, and harmonize Qi to avoid complications of itching and collapsing. In summary, pain is excess, itching is deficiency; mild heat causes itching, severe heat causes pain; both pain and itching belong to Fire, but their excess and deficiency differ significantly.

Saying "deficiency causes itching, excess causes pain" is a generalization. Emptiness inevitably causes itching, and itching inevitably leads to collapsing; this is logically inevitable. However, if the lesions are scorched-purple or ash-white, the condition is critical, and itching is inevitable. Thus, Qi deficiency causes itching, and Blood Heat also causes itching. Therefore, intervention at the time of swelling and rising is crucial: for Blood Heat, clear heat and cool Blood first; for Qi deficiency, tonify the Middle and boost Qi first. Then these complications will naturally be avoided. If treatment is delayed until symptoms are established, cure will be difficult. However, if the patient can eat or has hard stools, and scratched areas fill with pus again, while new eruptions appear elsewhere varying in size, even if all are scratched open, rescue is still possible. Conversely, during itching, if the patient is confused and restless, scratched areas do not fill with pus, form pits, become dry and black, or shed skin, accompanied by choking on water/food, inability to ingest liquids, diarrhea, loss of voice, chills with teeth grinding, cold extremities, abdominal distension, and crying, these are all fatal signs. However, if initially the lesions are sticky and the whole body itches, this indicates the pathogen desires to exit but is blocked by tight skin, causing wandering Fire, hence itching. This can be treated similarly to Sun-Yang Syndrome (Taiyang Disease) in Cold Damage presenting with body itching and no sweat: open the interstices to allow pathogen release; as the lesions rise, itching subsides. This embodies the principle of "dispersing stagnant Fire." If pus is fully formed and contraction begins, causing itching, this indicates the pathogen is scattering and Healthy Qi is recovering, harmonying Ying and Wei and Yang. This is similar to itching in other sores and boils nearing recovery; there is no need for worry, just remember not to scratch them open. During the stage of vigorous filling, when Blood transforms into fluid and fluid into pus, if the toxicity has not transformed and the whole body itches restlessly, this is a malignant sign. This is discussed similarly to the sensation of insects crawling in the skin in Yang-Ming Channel Cold Damage. This represents external assault by deficient Wind and internal strength of pathogenic factors. Itching of scars after scab fall is due to consumption of Ying Blood and dry skin, causing wandering floating Fire; severe Fire causes pain, mild Fire causes itching. Treatment should primarily clear Fire and nourish Yin. Generally, if eruptions are bright red and fleshy, or if they rise tenderly with much fluid, itching and collapsing will inevitably follow; preventive regulation is essential.

Itching and collapsing are causally linked; thus, collapsing does not necessarily mean itching, and itching does not necessarily mean collapsing. Itching without collapsing is treatable; collapsing without itching is treatable; simultaneous collapsing and itching is definitely difficult to treat. Scratching open like scalds is untreatable. Collapse with itching and no pus, indicating separation of Qi from Blood, is untreatable.