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The *Suwen* (Plain Questions), Chapter "Ci Zhi Lun" (Discourse on Needling and Pulse), states: "When the pulse is deficient and the body is hot, it results from injury by summerheat." It further states: "Summerheat is a Yang pathogenic factor." However, Li Dongyuan differentiated the treatment of summerheat into Yin-Yang and static-dynamic categories. Some individuals suffer from external invasion while seeking coolness in spacious, shaded buildings; others suffer from internal injury due to excessive consumption of raw and cold foods. The former, acquired during static rest, is termed Yin Summerheat; the latter, acquired during dynamic activity such as farmers plowing in fields or soldiers marching on roads, is termed Yang Summerheat. Yin Summerheat should be treated with warming methods, while Yang Summerheat should be treated with clearing methods. Zhao Yangkui stated that summerheat disease resembles heat disease, but the pulse in heat disease is full and forceful, whereas in summerheat disease, it is deficient. Generally, those injured by summerheat present with a soggy and weak pulse, or a string-tight, thin, hollow, or slow pulse. Their bodies are feverish, indistinguishable from common colds in any season. The distinguishing features are a red tongue, thirst, and scanty dark urine.

Regarding the manifestation of summerheat in the Five Zang Organs: The Heart belongs to Fire, so summerheat enters the Heart first. Summerheat damages Qi, and since the Lung governs Qi, excessive Fire insults Metal (the Lung). Furthermore, during late summer, damp earth is dominant. The Spleen dislikes dampness; when affected by summerheat, the Spleen's transformative and transporting functions fail. The Liver and Kidney share the lower Jiao and both contain Ministerial Fire. When the Liver is affected by summerheat, Dragon Fire arises; when the Kidney is affected, Thunder Fire ascends. With all five fires blazing fiercely, the situation is like a prairie fire spreading upward to the eyes, causing redness, nebulae, swelling, pain, and purulent discharge of eyes and tears. Treatment methods include using acrid-cool herbs to release the exterior and induce sweating, or clearing heat and nourishing Yin to promote urination, ensuring the summerheat pathogen is expelled outward without sinking inward and damaging Yin. If one is suddenly stricken by severe summerheat, cooling and resolving methods should be prioritized. For frail individuals lacking internal resistance who contract summerheat externally, cooling and resolving methods must be combined with supporting the healthy Qi, such as using Qing Shu Yi Qi Tang (Clear Summerheat and Boost Qi Decoction). Alternatively, if summerheat lies latent within and suddenly erupts during the storage phase of deep autumn, death may occur instantaneously, or it may damage Kidney Yin and harm the pupil. In such cases, cooling and tonifying True Yin is indicated immediately. Even if the latent summerheat has been stored for a long time but manifests slowly with red, swollen, and painful eyes during autumn and winter, summerheat-clearing formulas should still be used. Careful differentiation during clinical practice ensures that complex conditions can be managed effectively.