Over 90% of essential oils on the market are produced for nothing more than their fragrance and flavor. In other words, they are dead oils and absent of the constituents that would make them of therapeutic value. They may contain solvents, pesticides, fertilizers, synthetics and other chemicals!
Secondly, how that oil is extracted and handled from the moment a seed is put in the ground all the way through the moment it is bottled, has a direct impact on its effectiveness and therapeutic value. Cypress for example, has 280 known constituents. If distilled for 20 hours (even at the right pressure and temperature) you only get 20 of the 280 properties. If distilled for 26 hours you end up with 0 of the 280 potent properties. Only when this oil is distilled at the right temperature, with the right amount of pressure for exactly 24 hours, do you have an oil containing all 280 of its chemical constituents. This is why where you get your essential oils really does matter!