While natural food flavorings and/or perfumes make use of chemically modified oils in order to contain price or to compensate for a less than ideal plant year, in medicine, the wholeness of the essential oil is of paramount importance, regardless of the cost. It is not always recommended for aromatherapists to obtain their supply of essential oils from suppliers of the food and perfume industries because oils sold for these purposes may often be adulterated and are therefore not naturally whole in the manner that is expected for medicinal usage. Aromatherapists are cautioned to obtain naturally whole and unadulterated oils from reputable suppliers.

The aromatherapist - unlike the consumers of perfumes and foods - needs to acquire not merely a particular odor, but most importantly, the physicochemical characteristics of the particular oil. Essential oils are composed of specific natural chemicals, and many of these chemicals are found in other oils; therefore, it is not unusual for a chemist to remove a particular constituent from a cheaper oil and add it to a more expensive oil so as to lower the cost to the buyer, or to increase the profit based on selling a higher priced oil at a lower price. Adulteration also occurs when certain synthetic isolates are added, particularly to one of the more expensive essential oils such as rose otto. Alcohol and vegetable oil are good solvents for essential oils and are used at times to adulterate, stretch, or cut natural oils. The use of certain descriptive euphemisms are common in the food and fragrance industries. Imaginative euphemisms like "ennobled" are not uncommon in the descriptions of adulterated essential oils. Essential oils used in the fragrance industry are often stripped of their terpenes due to the insolubility of the terpenes in alcohol which results in cloudiness. Since the cloudiness makes the product aesthetically inferior to the consumer of perfume, the terpenes are removed. For the aromatherapist, however, the removal of these constituents makes the resultant oil incomplete, increasing the percentages of the remaining constituents of the oil.