Essential oils are the highly concentrated volatile extract of flowers herbs, grasses, shrubs and trees. These tiny droplets are present in particular glands, hairs or specific structures of the plant and contain some (but not all) of the active principles of the plant. Similar to herbal therapy principles, essential oils are phytochemicals with particular biological properties. Non-oily in texture, these highly concentrated substances are obtained by steam distillation, peel pressure, and solvent extraction methods. Only the utmost quality of essential oils should be used in aromatherapy.