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Sun Simiao stated: Throughout the four seasons, one should not sit or stand for long periods in damp and cold places. One should also not remove clothes or walk barefoot to cool off in the wind after becoming drunk from alcohol or sweating; all these behaviors can lead to Hongxiangjiao (Foot Qi disease).

If one sits or stands for a long time in damp and cold places during the hot summer months, the damp-heat qi will steam through the meridians and collaterals. Upon onset, the patient will inevitably experience fever, soreness and pain in the four limbs, and irritability.

If one sits or stands for a long time in damp and cold places during the cold winter months, the damp-cold qi will ascend into the meridians and collaterals. Upon onset, the four limbs will become extremely cold, accompanied by muscle spasms (Zhuanjin). There are scholars among the people who work diligently and study hard, sitting or standing for long periods on wet ground exposed to cold winds. Unaware of it, pathogenic factors invade the meridians and collaterals, causing illness. If one wishes to prevent this illness, at the first sign of discomfort, moxibustion should be applied to the affected area for 20–30 moxa cones (Zhuang), which will cure the condition and prevent fever. Huangdi said: Cooling off in the wind and engaging in sexual intercourse while drunk can cause this disease.

Li Dongyuan stated: The *Qianjin Fang* (*Essential Prescriptions Worth a Thousand Gold*), *Waitai Miyao* (*Secret Essentials of the Outer Terrace*), and *Zonglu* record that these conditions arise in southern regions characterized by low-lying terrain, dampness, fog, and dew accumulation. The local people have loose interstices (Couli) and their Yang qi fails to secure the exterior. Consequently, when they encounter such environments, clear-damp pathogens attack the deficient areas, and the disease originates from the lower body. This is due to weakened blood and qi, which allows clear-damp pathogens to invade and travel alongside the blood within the skin and interstices. When pathogens are strong and healthy qi is weak, blood and qi flow sluggishly, leading to Bi syndrome (obstruction); weakness leads to debility, resulting in Bi and weakness. Later generations named this condition Hongxiangjiao. The *Zhenjing* (*Classic of Acupuncture*) states: "It comes by a certain way, and it leaves by a certain way." Treatment often favors moxibustion to guide dampness outwards, along with drinking medicinal wine (Jiaoli) to unblock the meridians and scatter pathogens. Formulas prescribed contain few cold-natured herbs and many heat-natured herbs, primarily using Ephedrae Herba (Mahuang, 麻黄), Aconitum Kusnezoffii Radix (Chuanwu, 川乌), Zingiberis Rhizoma (Jiang, 姜), and Aconitum Carmichaelii Radix Praeparata (Fuzi, 附子). The *Neijing* states: "When dampness overflows internally, use bitter flavors to disperse it." Mahuang is bitter and warm, capable of dispersing dampness. Chuanwu is acrid and hot, moving without staying, circulating through the meridians. Jiang and Fuzi are acrid, sweet, and greatly hot, assisting Yang and retreating Yin, thereby also scattering clear-damp pathogens. Furthermore, one must observe which meridians the three Yin and three Yang meridians of the foot originate from, using them as guiding herbs for treatment. One must also examine which of the Six Qi pathogenic factors has invaded, using this to determine adjuvant and envoy herbs. Sun Simiao said: "The physician relies on intuition/understanding (Yi). Adjustments are made according to the season; there are no fixed formulas." These are truly profound words.

Differentiating the Etiology of Northern Hongxiangjiao

Invention states: The *Yifa Fangyi Lun* states: In the northern region, the land is high, with hills and mountains, where wind and cold are biting and ice is freezing. The custom involves drinking milk curds (Tongluo) and eating meat. Those who drink milk curds do so in large quantities and rapidly, which is detrimental. The Classic states: "Drinking excessively causes Qi to rebel"; it also says: "Food enters the Yin and generates Qi in the Yang." Now, however, it acts contrary to the Yin pathway, which is rebellious. Milk curds and strong wine are damp-heat substances belonging to drinks. Coupled with excessive nourishment, this further generates dampness. Water nature is moistening and tends downward; Yang Qi cannot ascend. Thus, dampness pours down to the shins and calves, accumulating over time to cause swelling, fullness, and pain. This results from the downward flow of diet. The *Tongping Xuushi Lun* states: "Abundant food intake but deficient Qi, with dampness residing below." Moreover, the damp-heat of milk curds and strong wine exceeds that of grains. The *Zhiyao Dayao Lun* states: "When Taiyin prevails, Fire Qi stagnates internally and flows outward, causing swelling of the feet and shins, fluid retention internally, and edema below." This refers to the process where water enters the Stomach, its essence spreads upward to the Spleen; the Spleen scatters the essence upward to the Lung; the Lung regulates the water passages, sending them downward to the Bladder; water essence distributes throughout, the five meridians circulate together, harmonizing with the four seasons and regulating the Yin-Yang of the five Zang organs as the norm. If diet doubles, the Spleen and Stomach are injured, causing Stomach Qi to fail in its distribution and Spleen Qi to fail in spreading. Consequently, dampness flows downward, attacking the Liver and Kidneys, and dampness flows into the shins and calves. Added to irregular sexual activity, Yang Essence is exhausted, and Yin becomes excessive, ultimately forming Hongxiangjiao. Sun Simiao said: Ancients rarely suffered from this disease. Since the southward migration during the Yongjia era, many scholars and officials have suffered from it, for this very reason.

Commentary: This statement indicates that Northern Hongxiangjiao is caused by Spleen dampness flowing downward, compounded by irregular sexual activity, and should be treated as an internal cause. This reveals the secrets of pathogenesis. However, Southern cases of this condition are also invariably caused by deficiency in the lower Jiao allowing pathogenic factors to invade. Chen Wuyue’s discussion on external contraction distinguishes between Wind-Damp-Cold-Heat and the excess-deficiency of the Five Internal Organs, prescribing treatment based on etiology, which far surpasses the text of *Qianjin Fang*. Why is this principle not fully elaborated here? Probably because this condition is rare in the North. Scholars who examine this will realize that Southern Hongxiangjiao cases exist that are entirely non-external in origin, as seen in examples like the Zi Su Zi Tang formula.