There are several types of fever in the world, each requiring different treatments. The key distinction lies between Exogenous Fevers (Exogenous Heat) and Endogenous Fevers (Endogenous Heat). However, both exogenous and endogenous fevers can be further classified into Deficiency (Xu) and Excess (Shi) patterns. Physicians must distinguish between them carefully.

For instance, fever caused by injury from cold pathogens is an Excess pattern where pathogenic factors invade the Wei (Defensive Qi) level and contend with Yang Qi, resulting in external heat. The pulse is tight and forceful. This occurs during mid-winter. Such fevers resemble those of Shanghan (Cold Damage). If cold is contracted in winter but does not manifest immediately, it may transform into Wenbing (Warm Disease) in spring, or Rebing (Heat Disease) in summer. Another type is epidemic plague fevers, which often occur between spring and summer, affecting households and neighborhoods uniformly. These are caused by epidemic qi from heaven and earth, irregular seasonal climates, and alternating cold and heat sensations. Some patients develop asthma; due to heat, breathing becomes coarse, and Qi fails to follow its normal course. Some patients experience vomiting because there is heat in the Stomach, causing Fire to flare upward. Some patients suffer from nasal congestion because heat lodges in the Yangming Meridian, causing nasal swelling.

Another type is a winter plague. Although treated at the wrong time, the climate is abnormal. It should be cold in winter, yet warm diseases occur instead. This is due to irregular heavenly timing, where Yang Qi leaks abnormally, causing heat. Another type is a seasonal cold epidemic occurring during a period of winter warmth. This is also due to irregular heavenly timing, where Yin Qi rebels abnormally, causing heat.

There is also heatstroke in summer. Although it belongs to exogenous causes, it resembles endogenous injuries and differs greatly from Shanghan. Cold damages the form; cold pathogens lodge on the exterior, constituting an Excess syndrome, so sweating therapy is appropriate. Summerheat damages Qi; Yuan Qi (Original Qi) is damaged by heat and dissipates. The pulse is deficient, slow, and weak, constituting a Deficiency syndrome. Additionally, due to summer heat, overconsumption of cold foods damages the interior, or excessive exposure to cold winds damages the exterior. In these cases, it is not summerheat directly injuring the person, but self-inflicted illness due to the summer environment.

Regarding dietary indiscretion and fatigue, internal injury to Yuan Qi leads to fever that may occur day and night, or be heavier by day and lighter by night, with no taste in the mouth. This is because Yang Qi is self-injured and cannot ascend to reach the Yin aspect, resulting in internal heat, which is a Yang Deficiency pattern. Thus, the pulse is large but weak, belonging to the Lung and Spleen.

Fever caused by sexual excess involves internal injury. Fever occurs in the afternoon until midnight, with a bad taste in the mouth. This is because Yin Blood is self-injured and cannot control Fire, allowing Yang Qi to surge upward, resulting in internal heat, which is a pattern of Yang Prosperity (Yin Deficiency with Fire Hyperactivity). Thus, the pulse is rapid but weak, belonging to the Heart and Kidney.

Injury to both Yin and Yang causes fever day and night, incessant irritability and thirst, and dry nose.

Internal injury from diet resembles early-stage Shanghan symptoms, but the right hand's Cun Kou pulse is tight and full, and the body does not ache, which distinguishes it.

Internal injury from overthinking causes mental confusion and恍惚 (trance-like state), red eyes, and fever.

Internal injury from raw/cold food causes obstruction of Yang Qi, leading to fever.

Consumption of mineral drugs, roasted/fried foods, sleeping near fire pits at night, or drying clothes near fire can accumulate heat toxins over time. A floating and large pulse indicates Excess Heat.

Destruction of Kidney Water allows Ministerial Fire to flare upward, causing dry mouth, irritability, thirst, shortness of spirit, and a fine/small pulse, indicating Deficient Heat.

There are Excess Heat in Qi, Excess Heat in Blood, and Combined Excess Heat in Qi and Blood. There are also Deficient Heat in Qi, Deficient Heat in Blood, and Combined Deficient Heat in Qi and Blood.

Bone-steaming fever is one type. Heart Heat involves heat in the blood vessels, worsening at noon, with red face, irritability, tendency to cry, spontaneous sweating from sores, hot palms, and dry mouth/tongue. Lung Heat involves heat in skin and hair, worsening in the evening, with upper asthma, cough, sore throat, shoulder/back pain, and epistaxis. Spleen Heat involves heat in muscles, worsening at night, with lethargy, desire to lie down, yellow face, abdominal distension, sweet taste with salivation, easy hunger but heavy body. Liver Heat involves heat below muscles and above bones, worsening during Yin-Mao hours (3-7 AM), with hypochondriac pain, eye pain, tearing, cheek swelling, dizziness, tendon stiffness, and anger. Kidney Heat involves heat between bones, worsening during Zi-Chou hours (11 PM-3 AM), with burning soles, excessive sleep, dysuria, dry mouth, and foot edema.

Five-center heat (palms, soles, chest) indicates Yin Deficiency with Fire Hyperactivity. Chest irritability with dizziness and dry mouth indicates internal Heart irritability without external heat.

One must still distinguish Deficiency and Excess. If caused by excessive loss of fluids after sweating, vomiting, or purging, leading to dryness of the five zang organs, it belongs to Deficiency. If not caused by these methods, it is Excess.

Tidal fever: If fever occurs at Dibu (3-5 PM) in Shanghan, it indicates Stomach Excess, with no other deficiency symptoms. Other cases require careful examination of Deficiency and Excess.

As mentioned earlier, isolated facial heat indicates abundant Qi in the Yangming Meridian or rising Wind-Heat.

Accumulation diseases most commonly cause fever, often with severe abdominal heat at night.

The Classic states: "Treating disease requires seeking the root." Wind-Heat, Phlegm-Heat, and Damp-Heat are the roots of hundreds of diseases and must be examined in detail.

Wind-Heat causes head/eye swelling/pain, vertigo, blurred vision, red eyes, deafness, nasal congestion, dry mouth/tongue, macules/rashes—results of Wind-Heat flaming upward.

Phlegm-Heat causes sore throat, throat closure, diaphragmatic blockage, chest stuffiness, mania, palpitations—results of Phlegm-Fire stagnating in the Middle Jiao.

Damp-Heat causes diarrhea, dysentery, edema, drum-like distension, jaundice, spermatorrhea, leukorrhea, hernia, Hongxiangjiao (Beriberi/Foot Rot), waist/knee pain—results of Damp-Heat flowing downward.

For mild heat, use cool properties to harmonize. For severe heat, use cold properties to consolidate. For extreme heat, use sweating to disperse. For internal heat, use purgation. For external heat, use sweating. For deficiency, use tonification. Thus, errors will be avoided.