This suggests that the pathological change or damage leading to deficiency of either yin or yang will further involve the other,and form deficiency of yin and yang. It includes yin damage tending to yang and yang damage tending to yin.
* Yang damage tends to yin
When the deficiency of yang interferes with the production of yin fluid and leads to a deficiency of yin, that forms the deficiency of both yin and yang with domination of yang.
* Yin damage tends to yang
When the deficiency of yin interferes with the production of yang and leads to an insufficiency or exhaustion of yang ,that forms the deficiency of both yin and yang with the domination of yin.
Because the kidney is the root of yin and yang of the body ,so mutual damage of yin and yang mostly come from the damage of the kidney by other Zang organs.