When measles first appear with fever, vomiting, and diarrhea, it is purely a heat syndrome and should not be treated as a cold syndrome. This is due to fire pathogen forcing inward: affecting the Upper Jiao (Upper Burner) leads to frequent vomiting; affecting the Lower Jiao (Lower Burner) leads to frequent diarrhea; affecting the Middle Jiao (Middle Burner) results in both vomiting and diarrhea. For pure diarrhea, Huangqin Tang (Scutellaria Decoction) is appropriate. For simultaneous vomiting and diarrhea, Huangqin Tang added with Banxia (Pinellia Rhizome) and Shengjiang (Fresh Ginger) is appropriate. For pure diarrhea accompanied by tenesmus (urgency and straining with little discharge), Lianhuang Jiedu Tang (Coptis Detoxification Decoction) combined with Yiyuan San (Benefit Prime Powder) is appropriate.

If one or two days, or three to four days after the eruption of measles, sudden severe diarrhea occurs with increased coughing, treatment should involve herbs that lift and vent the exterior, combined with methods to separate turbidity and promote urination. If diarrhea is accompanied by wheezing, along with restlessness and head-shaking, the prognosis is ominous.

After the manifestation of measles, if pus and blood appear in the stool, or if diarrhea transforms into pus and blood, or if there is spontaneous diarrhea, provided the rash is abundant and red in color and accompanied by significant coughing, only the method of venting the rash should be employed. Only after the rash has subsided should detoxification be applied, while simultaneously treating the diarrhea.

Diarrhea is most contraindicated at the initial stage of measles. However, there are cases where diarrhea persists throughout without hindering recovery, depending on the strength of the patient's constitution. If diarrhea causes the cough to subside but transforms into wheezing, the condition becomes critical; see the section on wheezing and coughing for details.

For symptoms of body heat, irritability, thirst, and diarrhea, Chai Ling Tang (Bupleurum and Poria Decoction) or Siling San (Four-Poria Powder) may be used. If the heat is severe or during summer months, Yiyuan San (Benefit Prime Powder) is suitable.

After measles recede, diarrhea may present with signs such as observing hands, biting nails, tearing lip skin, or biting others. These should be treated with drugs that detoxify and separate turbidity. If the discharge consists of thick saliva mixed with red and white substances, detoxifying drugs must definitely be used. If diarrhea occurs twenty to thirty times a day and night, gradually decreasing to two or three times, or if coughing gradually increases, the pulse at the first finger of the right hand gradually becomes palpable, and clear nasal discharge returns, survival can be hoped for. If the excrement turns the color of coal dust, the color of old tubercular ulcers (fanglou), or the color of green vegetables; if the anus becomes flaccid like a straight tube; if there is rapid breathing, hoarseness, inability to eat or drink, and redness of the cheeks in the afternoon, these are all incurable conditions.

Zhang Jingyue stated: In ancient medical texts, there are occasionally instances where explanations are incomplete or treatments are inappropriate. This is particularly true regarding diarrhea. Why? Because ancients believed nine-tenths of diarrhea cases were heat-related, thus often using Liu Hejian’s Huangqin Shaoyao Tang (Scutellaria and Peony Decoction) as the primary treatment, unaware that most diarrhea stems from Spleen and Kidney deficiency-cold. Taking measles as an example, although some diarrhea is caused by measles toxin, genuine excess-heat syndromes rarely cause diarrhea. Those that do cause diarrhea are mostly due to Spleen and Stomach weakness. If one only knows how to clear fire and detoxify, the Spleen and Stomach earth will deteriorate daily, gradually leading to incurable conditions such as fanglou, vegetable-green stools, shortness of breath, and cessation of food intake. At this stage, is it still a heat syndrome? It is entirely a misdiagnosis. (De notes: Ma Yuanyi said acute diseases are mostly excess, chronic diseases are mostly deficiency, incontinence is mostly cold, and stagnation is mostly heat. Combining pulse and symptom analysis yields near-perfect accuracy.) Therefore, when treating diarrhea, even in the context of measles, one must examine whether heat pathogen exists. If there are no heat signs or heat pulses, one should seek treatment methods from the section on chickenpox/measles-related diarrhea. Thus, even the most critical cases may have hope for survival. This is why I emphasize these key points beyond other methods.