Whatever found in the universe is divided into Yin (negative) and Yang (positive). They are the two principles which oppose one another in their actions. They are the two fundamental opposing concepts in Chinese philosophy. The universe is divided into day and night, summer and winter, man and woman, etc same goes with essential oil with Yin and Yang characteristic.

Normally, man has the characteristic of Yang whereas woman has the characteristic of Yin.

To restore the health means restore the balance the Yin & Yang energy.

An accurate way to use aromatherapy is to select an appropriate essential oil to balance the Yin and Yang energy in one's body accordingly. Each of the essential oil has it's own Yin or Yang nature.