Ancient Chinese philosophers explained the constant changes they observed in every aspect of the world as the result of the dynamic movement and mutual opposition of what they termed Yin and Yang factors. In TCM, the theory of Yin-Yang is used to explain physiological activities and pathological changes in the human body, and to guide clinical treatment strategies.
The philosophical Theory of Yin-Yang holds that every object or phenomenon includes two opposite aspects that are referred to as the yin or the yang factors. Examples are down and up, left and right, dark and light, cold and hot, and still and moving, although there are many more.
In TCM, anything that is organic, still, descending, dark, degenerating, or hypoactive is classified as yin; and anything that is functional, moving, ascending, bright, progressing, hyperactive, or hot is classified as yang. Furthermore, everything that is yin is also further divisible into yin and yang, just as everything that is yang is further divisible into yin and yang. Neither yin nor yang ever exists in isolation, and each also contains the other. The taiji symbol is an illustration of the Theory of Yin-Yang.
Yin and yang are always opposing each other, and therefore, they are constantly interacting and restricting each other. They are also interdependent in that they rely on each other for existence. and neither can exist without the other. Therefore, they are also mutually consuming and mutually engendering. Under certain circumstances, they are capable of transforming to the opposite, in which case yin will become yang, and yang will become yin. This is often seen in illness where a yang febrile disease will transform into a yin cold one.
In addition to being used to describe the nature or stages of illness and pathological developments, the Theory of Yin-Yang is also used in TCM to categorize anatomical aspects, such as interior/exterior, lower/upper, front/back, left/right, medial/lateral; and to distinguish physiological structures from their physiological functions. In formulating treatment strategies, imbalance between Yin-Yang is one of the fundamental concepts used to discern the various causes of illness and to determine appropriate therapeutic approaches.
Yin congestion due to the inability of Yin to harmonize with Yang. Symptoms can include muscle stiffness and spasm, stomach pain, and diarrhea.
A condition of exhausted or weak Yin whereby Yang is in relative abundance. Severe Yin Deficiency can cause too much Heat or Fire. Symptoms can include flushed cheeks, fatigue, hot flashes, night sweats, dry mouth, dry skin, vaginal dryness, ear ringing, dizziness, insomnia, palpitation. Individuals with Yin Deficiency may become easily agitated or anxious. The pulse is commonly thin and fast; the tongue is often red and thin with scant or absent coating; the nails are usually.
When Yang is exhausted or weak, Yin is in relative abundance. Symptoms can include paleness, tendency to feel cold, weakness, tendency toward lower back pain, and diarrhea. The pulse is often deep, thin, weak and slow; the tongue and nails are often pale.