Although severe heat in Shanghan (Cold Damage) is not necessarily fatal, two-gan Shanghan (simultaneous infection of exterior and interior meridians by cold pathogen) is difficult to manage. (Zhang Zhongjing stated: "Whenever one is injured by cold, it manifests as heat; even if severe, it is not fatal. However, if one suffers from two-gan due to cold, death is inevitable." He further said: "When two-gan occurs, both exterior and interior are affected simultaneously. Treatment must follow a sequence of priority; releasing the exterior and purging the interior are fundamentally different approaches. Thus, it is described as difficult to manage.")

On the first day, Taiyang (Greater Yang) and Shaoyin (Lesser Yin) diseases occur together, presenting with abdominal pain, dry mouth, irritability, and thirst for water. (Taiyang corresponds to the Bladder, and Shaoyin corresponds to the Kidney; they are exterior-interior pairs. Hence, Zhang Zhongjing stated: "When Taiyang and Shaoyin are diseased together, there is abdominal pain, dry mouth, irritability, fullness, and thirst.")

On the second day, Yangming (Yang Brightness) and Taiyin (Greater Yin) diseases combine, characterized by abdominal distension, body heat blazing like fire, anorexia, dryness inside the nose, delirious speech, and ultimate insomnia. (Zhang Zhongjing stated: "On the second day, when Yangming and Taiyin are diseased together, there is abdominal distension, body heat, aversion to eating, and delirium.")

On the third day, Shaoyang (Lesser Yang) and Jueyin (Terminal Yin) diseases combine, manifesting as deafness, retraction of the testicles, loss of consciousness, cold extremities, and inability to swallow fluids. The sixth day marks the time of death. (Zhang Zhongjing stated: "On the third day, when Shaoyang and Jueyin are diseased together, there is deafness, retraction of the testicles, and cold extremities; inability to take in fluids and loss of consciousness indicate death will occur on the sixth day.")

The transmission among Taiyang, Yangming, and Shaoyang constitutes the normal progression of these three Yang meridians. (Day 1-2 involves Taiyang; Day 2-3 involves Yangming; Day 3-4 involves Shaoyang; each transmits according to its meridian.) Taiyang presents with a floating pulse, aversion to cold, and aversion to wind. Yangming presents with aversion to heat and a long pulse. (Taiyang pulse is floating; Yangming pulse is long. Taiyang has aversion to cold and wind; Yangming lacks aversion to cold but has aversion to heat.) Shaoyang presents with bitter taste, hypochondriac fullness, alternating chills and fever, and a wiry pulse. (Zhang Zhongjing stated: "The disease of Shaoyang includes bitter taste, dry throat, and vertigo." He also said: "If Taiyang disease does not resolve and transfers to Shaoyang, there is hardness and fullness below the costal region, alternating chills and fever, and a thin-wiry pulse.") If Yang qi becomes excessively dominant while Yin qi suddenly perishes, it transforms into Yang Du (Yang Toxin), inevitably leading to mania. (Untreated diseases of the three Yangs will inevitably transform into Yang Du.) With internal and external heat binding, the tongue curls, and soot-like blackness appears in the nostrils, which is unbearable. The pulse should be surging and solid or slippery and rapid. Shengma Zizi Tang (Cimicifugae Rhizoma and Gardeniae Decoction) is indicated.