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This refers to illness caused by exposure to cold pathogenic factors. During the severe cold of winter, those who carefully maintain their defensive qi (Wei Qi) will not be harmed by the cold. However, if one suddenly suffers from overexertion and labor, sweats, and then is exposed to cold air, illness will immediately manifest; this is called Cold Damage (Shanghan). In mild cases, symptoms include slight coughing, nasal congestion, shivering chills, and low-grade fever, which resolve after a few days. In severe cases, symptoms include headache, body aches, aversion to cold, and high fever. Plump individuals with fragile skin and muscles are prone to cold injury even without obvious exposure, provided there is any minor impropriety in their living environment or daily routine. When sudden violent cold occurs during normal seasonal transitions, causing illness upon exposure, it is also named Cold Damage, specifically referred to as Epidemic Cold Damage (Shixing Shanghan). This is not caused by personal exposure but indicates that this specific pathogenic factor is prevalent at that time, hence the term "Epidemic" (Shixing).

This refers to illness caused by abnormal climatic conditions appearing suddenly during the four seasons. For instance, spring should be warm but turns cold; summer should be hot but turns cool; autumn should be cool but turns hot; winter should be cold but turns warm. It signifies that this abnormal climate prevails during these periods. Once such climate arrives, regardless of age, the resulting illnesses present similar symptoms, thus termed Seasonal Qi (Shiqi) disease. Regarding the severity: if caused by wind-cold, the condition is milder, resembling Cold Damage with slight headache and high fever. If complicated by toxic and pestilential qi, the condition is severe, presenting with high fever, restlessness, toxicity, abdominal distension and fullness, often leading to death.

Malaria (Nue Bing) arises from summerheat injury in summer, where the pathogen resides in the skin. In autumn, due to physical exertion depleting blood and qi, the interstices (Cou Li) become deficient, allowing wind pathogen to invade. This triggers the latent summerheat, causing righteous qi and pathogenic factors to clash. Yin and Yang engage in conflict: excess Yang leads to heat, excess Yin leads to cold. As Yin and Yang alternate between deficiency and excess, chills and fever ensue. When Yin and Yang separate (the struggle ceases temporarily), both chills and fever subside. If the pathogen reactivates and righteous qi responds again, the clash recurs, causing malaria to have periodic intervals of onset and remission.

When the onset time gradually delays, it is because the pathogen lodges in the Fengfu acupoint (GV16) and moves downward along the spine. Defensive Qi (Wei Qi) gathers at Fengfu once every day and night. The next day, it descends one vertebral level, causing the onset time to delay daily. When the onset time advances earlier, it is because Defensive Qi travels past Fengfu, descending one level daily. After twenty-one days, it reaches the coccyx; on the twenty-second day, it enters the interior of the spine, ascends into the Fu Chong vessel, travels upward for nine days, and emerges within the Quepen area (LI15 region). Since the qi has ascended, the disease manifests earlier.

For intermittent malaria occurring every other day, the pathogen presses inward toward the five zang organs and extends laterally to the Mu Yuan (sea of origin). The pathway is distant, the pathogen is deep, and its movement is slow, preventing daily attacks. Thus, it accumulates until sufficient force builds up before manifesting.

Generally, patients with malaria experience thirst and desire to drink. If the ingested water fails to transform and dissipate, it may form phlegm-stagnation masses (Pi). If large intestine deficiency leads to thirst and drinking, the water entering the stomach and intestines transforms into diarrhea.