Essential oils, or essences, are highly concentrated substances which contain active substances extracted from various parts of aromatic plants and trees. Essential oils are produced by tiny glands in the petals, leaves, stems, bark and wood of many plants and trees. These oils are often confused with herbal oils or floral oils but they are in fact very different. Although herbal oils have various cosmetic uses and are 12 good for massage, they lack the ethereal and concentrated nature of essential oils and cannot substitute them.