Chinese five elements theory refers to the five element of wood, fire, earth, metal, and water. This theory can be used to describe the movement and the relationship between different elements and phenomena in nature.

Basic five elements characteristics and classifications

The Cycles

Promoting Cycle
This cycle is explained most easily by a simple metaphor. The relationship is the same as a mother and child relationship, where the child is dependent upon the mother for nourishment and therefore growth and well-being.

Controlling Cycle
To understand the relationship of the controlling cycle, we must look more closely at the origin of the five element theory in China where the responsibility of disciplining the children rested with the grandparents. The controlling cycle describes the relationship of a grandmother disciplining a grandchild.

Over-controlling and Counteracting
Over-controlling means that an element is too strong/hyperactive and is controlling the other element too much. A common condition in which the wood element controls earth too much (or overacts) will manifest itself with symptoms of hyper wood as well as hypo earth, sometimes making the deficient-earth element even more deficient. Counteracting is the reverse situation--a controlled element is rebelling against its controlling element.

Diagnosis According to Five Element Theory
The colors, emotions, flavors, senses, climates, body parts, and organs are all related. Through viewing the human body in this way, we can determine internal disharmony. For example, if a patient has a green hue to his complexion, a sour taste in his mouth, and his eyes are bothersome to him in some way, we would look more closely at the Wood element (Liver and Gallbladder).

from  http://www.orientalmedicine.com/bt_five_elems.htm