This pertains to the degree of yin and yang, ranging from cold (extreme yin), cool, neutral to warm and hot (extreme yang).
The patient’s internal balance of yin and yang is taken into account when the herbs are selected. For example, medicinal herbs of “hot”, yang nature are used when the person is suffering from internal cold that requires to be purged, or when the patient has a general cold constituency.
Sometimes an ingredient is added to offset the extreme effect of one herb.