An essential oil is a concentrated, hydrophobic (not soluble in water) liquid containing volatile aroma compounds mainly from plants. Essential oils are also known as volatile or ethereal oils. An oil is "essential" in the sense that it carries a distinctive scent, or essence, of the plant. Essential oils do not as a group need to have any specific chemical properties in common, beyond conveying characteristic fragrances.
Essential oils are generally extracted by distillation. Other processes include cold pressing, or solvent extraction. As they often have an odor, they are used in perfumes, cosmetics, soap and other products, for flavoring food and drink, and for scenting incense and household cleaning products. Typically, essential oils are highly complex mixtures of often hundreds of individual aroma compounds.
Various essential oils have been used medicinally at different periods in history. Medical application proposed by those who sell medicinal oils range from skin treatments to remedies for cancer, and are 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 volatilized or diluted in a carrier oil and used in massage, diffused in the air by a nebulizer or by heating over a candle flame, or burned as incense.