These two terms are used varyingly in Chinese Medicine. They both signify change, change in pathology, or transition of the state of the body. They are not however used interchangeably. Bian, according to Wiseman, defines it as a major transmutation. Used in the Shan han lun, Bian zheng, it states a conversion of pattern from polar shift of state. Through improper use and diagnosis, a repletion can change to a depletion due to an inappropriate treatment. An outward change is shown, in a symptomatic systemic change in the body. For example an excessive fire needle treatment to a cold damage, can cause an excess, with palpitations and oppression in the chest where there was a deficiency. It is also used in transmutational patterns from one of the six levels to another.
Hua on the other hand, is an internal essential change. It is usually used in processes of the body. In describing the ripening of food in the digestive tract, Hua, is the change from a food particular to a nutrient. It is the process of change from ingested water to urine. It is the change of an external influence into an internal manifestation. Such as in the introduction of an external invasion, that stagnates the body’s qi, that qi in turn may transform into heat, fever, and the like.
“Bian tends to be associated with form (xing) and hua with matter (zhi). When a snowman melts, the form changes (bian) as the snow melts, hua, to water.” In chinese medicine one would use herbs or points that would help transform, Hua, a phase of the body, such as heat, water, or wind into another phase, where as bian would be more of a systemic outward change in pattern of the body, or state of health.