It is important to note that the more an essential oil is interfered with chemically or physically the more the therapeutic powers are reduced. Some oils have more than one or two of these properties. Each essential oil depends upon the balance of its constituents for its perfume and therapeutic effect. It is this balance which makes the oil more or less toxic than another. The constitutes of this oil or when combined, those of another may make the oil less toxic and more suitable for therapeutic use.
Essential oils are often mixed with other essential oils to make a blend.
When blending essential oils, it is important to consider their volatility or high rate of evaporation. Some oils have a much higher rate of volatility that others. Top notes are fastest acting, the quickest to evaporate and the most stimulating and uplifting. Middle notes are not as volatile and primarily affect the functions of the body eg digestion, menstruation etc, while the base notes are slow to evaporate and are most sedating and relaxing. As referred to earlier, essential oils can assist the body in more than one way.