An essential oil is a concentrated hydrophobic liquid containing volatile aromatic compounds from plants. Some plants like the bitter orange are sources of several types of essential oils. Essential oils are generally extracted by distillation or solvent extraction. They are used in perfumes cosmetics and bath products for flavouring food and drink and for scenting incense and household cleaning products. Various essential oils have been used medicinally at different periods in history. Medical application proposed by those who sell medicinal oils ranges from skin treatment to remedies for cancer and is often based on historical use of these oils for these purposes. Such claims are now subject to regulation in most countries and have grown more vague to stay within these regulations. Interest in essential oils has revived in recent decades with the popularity of aromatherapy a branch of alternative medicine which claims that the specific aromas carried by essential oils have curative effects. Oils are volatillsed or diluted in a carrier oil and used in massage diffused in the air by a nebuliser or by heating over a candle flame or burnt as incense.