An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils or ethereal oils. An oil is “essential” in the sense that it carries a distinctive scent, or essence, of the plant. Essential oils are generally extracted by distillation. Steam distillation is often used. Other processes include expression or solvent extraction. Interest in essential oils has revived in recent decades with the popularity of aromatherapy, a branch of alternative medicine that claims that essential oils and other aromatic compounds have curative effects. Essential oils have been used as perfumes for centuries, such as Sandlewood, Patchouli, Myrrh, Saffron, Frankincense and many others.