What are the Three Causes of disease in TCM?

The Three Causes theory (三因学说, Sān Yīn Xué Shuō) was systematized by Song Dynasty physician Chen Wuze (陈无择) in his text San Yin Ji Yi Bing Zheng Fang Lun (三因极一病证方论, c. 1174 CE). It classifies all causes of disease into three categories: (1) External causes — the Six External Pathogens (Wind, Cold, Heat, Dampness, Dryness, Summer Heat) that invade from outside the body. (2) Internal causes — the Seven Emotions (Joy, Anger, Worry, Overthinking, Grief, Fear, Fright) that arise from within and disrupt organ Qi. (3) Neither-internal-nor-external causes — lifestyle factors including improper diet, overexertion, excessive rest, trauma, and sexual excess. This framework provides a complete etiological system that guides diagnosis and treatment.

How is this different from the Western germ theory of disease?

Western germ theory identifies specific pathogens (bacteria, viruses) as the primary cause of infectious disease. TCM's Three Causes theory is broader and more holistic: it asks not just 'what entered the body' but 'what allowed disease to take hold.' A pathogen can only cause illness if the body's Zheng Qi (upright Qi, roughly equivalent to immune resilience) is weak enough to allow it. The same external wind-cold pathogen might cause a cold in one person and no symptoms in another, depending on their internal state. TCM also considers emotional and lifestyle causes as equally important as external pathogens — something Western medicine is only beginning to acknowledge through psychoneuroimmunology.

The Three Causes of Disease in TCM (三因学说): Understanding How Illness Begins

What Are the Three Causes?

The Three Causes Theory (三因学说, Sān Yīn Xué Shuō) is TCM’s comprehensive framework for understanding why people get sick. Systematized by the Song Dynasty physician Chen Wuze (陈无择) around 1174 CE in his text San Yin Ji Yi Bing Zheng Fang Lun, it organizes all disease causes into three categories:

Category	Chinese	Causes
External	外因	Six Pathogens: Wind, Cold, Heat, Dampness, Dryness, Summer Heat
Internal	内因	Seven Emotions: Joy, Anger, Worry, Thought, Grief, Fear, Fright
Neither internal nor external	不内外因	Diet, lifestyle, trauma, overexertion

This framework teaches that disease never arises in isolation — it results from the interaction between a pathogenic factor and the body’s vulnerability. The Huangdi Neijing summarizes this principle:

“When Zheng Qi (upright Qi) is strong, pathogenic factors cannot invade. Where pathogenic factors gather, there must be deficiency of Qi.”

First Cause: The Six External Pathogens (外因 — 六淫)

The six climatic factors — Wind, Cold, Heat, Dampness, Dryness, and Summer Heat — are normal aspects of nature. They only become causes of disease when they are excessive, unseasonal, or the body is too weak to adapt. When this happens, they are called “Six Evils” (六淫) — excessive climatic Qi.

1. Wind (风)

Nature: Yang pathogen, light and moving
Characteristics: Comes and goes quickly, migrates, causes symptoms that change location
Common symptoms: Headache that moves around, aversion to wind, wandering joint pain, sneezing
Role: The “leader of 100 diseases” — Wind often carries other pathogens into the body
Season: Spring (but can occur in any season)

2. Cold (寒)

Nature: Yin pathogen, damages Yang
Characteristics: Causes contraction, stagnation, and pain
Common symptoms: Severe pain that improves with warmth, cold limbs, abdominal pain, contraction of muscles and tendons
Season: Winter

3. Summer Heat (暑)

Nature: Extreme Yang pathogen, only occurs in summer
Characteristics: Consumes Qi and fluids, rises upward
Common symptoms: High fever, profuse sweating, thirst, fatigue, fainting
Season: Summer only

4. Dampness (湿)

Nature: Yin pathogen, heavy and sinking
Characteristics: Causes heaviness, sluggishness, sticky symptoms that linger
Common symptoms: Heavy limbs, lethargy, sticky mouth, edema, joint swelling, vaginal discharge
Season: Late summer

5. Dryness (燥)

Nature: Consumes fluids
Characteristics: Causes dryness in all body tissues
Common symptoms: Dry skin, dry cough, dry throat, dry stool, cracked lips
Season: Autumn

6. Fire/Heat (火/热)

Nature: Yang pathogen, flares upward
Characteristics: Causes redness, heat, agitation, rapid pulse
Common symptoms: Fever, red eyes, red face, irritability, mouth ulcers, bleeding, rapid pulse
Season: Can occur in any season

Pathogenic Combinations

External pathogens rarely attack alone. Common combinations:

Combination	Symptoms
Wind-Cold	Chills, headache, body aches, no sweating
Wind-Heat	Fever, sore throat, yellow phlegm, slight sweating
Wind-Damp	Wandering joint pain, heaviness, sticky sweat
Cold-Damp	Joint pain that worsens in damp weather, digestive heaviness
Damp-Heat	Yellow discharges, burning sensations, skin eruptions
Wind-Dryness	Dry cough, dry skin, dry throat in autumn

Second Cause: The Seven Emotions (内因 — 七情)

Emotions are normal human experiences. They become causes of disease only when they are excessive, prolonged, or suppressed. Each emotion directly affects a specific organ:

Emotion	Chinese	Affected Organ	Effect on Qi
Joy	喜	Heart	Slows and scatters Qi
Anger	怒	Liver	Rising Qi
Worry	忧	Lung	Binds and knots Qi
Overthinking	思	Spleen	Knots Qi
Grief	悲	Lung	Consumes Qi
Fear	恐	Kidney	Descends Qi
Fright	惊	Heart	Scatters Qi

The Mechanism: Emotions Disrupt Qi Movement

Each emotion has a characteristic effect on the direction and quality of Qi:

Anger makes Liver Qi rise — headache, red face, irritability
Joy makes Heart Qi scatter — restlessness, palpitations, insomnia
Worry makes Lung Qi bind — chest tightness, sighing, shallow breathing
Overthinking makes Spleen Qi knot — poor appetite, bloating, fatigue
Grief consumes Lung Qi — shortness of breath, fatigue, crying
Fear makes Kidney Qi descend — lower back pain, bedwetting, insecurity
Fright scatters Heart Qi — palpitations, mental disorientation

Why Suppressed Emotions Are Worse

In TCM, suppressing emotions is considered more harmful than expressing them. When emotions are held in, they create Qi stagnation, which over time transforms into Heat, Phlegm, or Blood Stasis. The classical texts advise:

“When angry, one should express it. When sorrowful, one should weep. Holding them in is the root of many diseases.”

Third Cause: Neither Internal Nor External (不内外因)

This category covers lifestyle and environmental factors that don’t fit neatly into external (climatic) or internal (emotional) categories:

1. Improper Diet (饮食不节)

Overeating: Food stagnation, dampness, obesity
Under-eating: Qi and Blood deficiency
Excessive raw/cold food: Damages Spleen Yang, causes diarrhea and cold pain
Excessive spicy/greasy food: Creates damp-heat, acne, digestive issues
Excessive alcohol: Creates damp-heat, damages Liver
Irregular eating times: Weakens Spleen and Stomach rhythm

2. Overexertion and Excessive Rest (劳逸失度)

Overexertion (过劳):

Physical overwork depletes Qi — chronic fatigue, muscle weakness
Mental overwork depletes Heart Blood and Spleen Qi — insomnia, poor memory
Sexual excess depletes Kidney Jing — lower back pain, premature aging, infertility

Excessive rest (过逸):

Lack of movement causes Qi and Blood stagnation
Obesity, sluggishness, weak muscles
Poor circulation

3. Trauma and Injury (外伤)

Physical injuries (falls, cuts, fractures)
Animal bites and insect stings
Burns and frostbite
Surgery and medical procedures

4. Poisonous Substances (中毒)

Food poisoning
Drug toxicity
Environmental toxins
Poisonous plants and animals

The Disease Process: How Causes Lead to Illness

TCM doesn’t view the Three Causes as directly causing disease. Instead, disease arises from the interaction between the pathogenic factor (Xie Qi) and the body’s resistance (Zheng Qi):

Pathogenic Factor (Xie Qi)  +  Body's Vulnerability (Zheng Qi deficiency)
                    ↓
                    Disease

This explains why:

Not everyone in a cold room catches a cold — those with strong Wei Qi (defensive Qi) resist
Not everyone under stress gets sick — those with smooth Liver Qi adapt
The same food that nourishes one person may cause problems for another

The Key Principle: Zheng Qi vs. Xie Qi

Factor	Meaning	Role
Zheng Qi (正气)	Upright Qi — the body’s healthy resistance	Determines vulnerability
Xie Qi (邪气)	Pathogenic Qi — the disease-causing factor	Triggers the illness
Strong Zheng Qi	Healthy immune function	Xie Qi cannot invade
Weak Zheng Qi	Compromised immunity	Xie Qi finds an opening

Treatment therefore has two goals:

Strengthen Zheng Qi — tonify the body’s resistance
Eliminate Xie Qi — expel the pathogenic factor

Historical Significance

Chen Wuze’s Three Causes framework was revolutionary because it:

Organized all previously scattered etiological knowledge into one system
Clarified that emotional and lifestyle factors are as important as external pathogens
Guided treatment — knowing the cause determines the therapeutic strategy
Prevented reductionist thinking — reminding practitioners to consider all three categories

This 12th-century framework anticipated what modern medicine now calls the biopsychosocial model — the understanding that disease results from biological, psychological, and social/lifestyle factors combined.

Key Takeaways

The Three Causes theory classifies all disease causes: External (6 pathogens), Internal (7 emotions), and Lifestyle factors
External pathogens are normal climatic factors that become pathogenic when excessive or the body is vulnerable
Each of the 7 emotions directly affects a specific organ and disrupts Qi movement in a characteristic way
Diet, exercise, rest, and trauma form the third category — lifestyle factors
Disease arises from the interaction between pathogenic factors and the body’s resistance (Zheng Qi)
Strengthening Zheng Qi is as important as expelling pathogens — prevention is the highest medicine

Disclaimer: This article is for educational purposes only. For health concerns, consult a qualified healthcare professional.