The key principle in Chinese medicine is that everything is part of a whole. To understand one part, it must be in relationship to the whole. This becomes quite helpful in understanding your health. Your skin problem might help us understand more about your digestion, for example. Your digestion might help us diagnose your headaches or sleep issues.
This wholeness is represented by the concepts of Yin and Yang. These are labels for describing complementary opposites that are always present in relatively different proportions. The balance between Yin and Yang can explain patterns, change, and relationships.
One basic way of understanding the two is to say that Yin is form and Yang is function. Yin is material, substance, cool, dark, moist, heavy, quiet in relationship to Yang, which is immaterial, light, warm, dry, active. But think of these qualities not as lists but as relative to each other. For instance, the upper body is relatively Yang compared to the lower body. But the back of the upper body is more Yang than the front of the upper body. Similarly, the inner organs are more Yin than the outer (skin).
The familiar Tai-Ji symbol of Yin-Yang is instructive:
This whole has both a Yin aspect and a Yang aspect. Yin is the dark; Yang, the light. The circle would not be complete without both aspects. This is true in the 24-hour cycle of light and dark. It is also true in our bodies.
Another part of Yin-Yang theory that is illustrated in the symbol is that within Yin there is a bit of Yang and vice versa. The small dot of the opposite color shows that one will always transform into the other. You see this law of nature at work in health. Your cold might start off with a fever (Yang) but then transform into chills (Yin). We use this understanding of nature to read your symptoms and body and help make appropriate suggestions for healing.