Eventually the circulating oils must pass through the liver, which is an organ situated in the lower-right side of the thorax, below the ribcage. The liver is thought to be the primary site of essential oil metabolism within the body. Metabolism is a term that refers to the life-sustaining chemical reactions occurring within living cells that provide for growth, reproduction, resiliency, and response to the environment. When the essential oil moves into the liver, specialized enzymes work to break down individual compounds into metabolites. These metabolites continue to circulate within the body before being eliminated, primarily in urine (1). Some essential oil metabolites may also be eliminated in the feces, through the skin, or exhaled from the lungs (2).
Many essential oil metabolites have been found to be biologically active and contribute their own favorable effects. For example, one study explored how limonene, the primary constituent in many citrus oils, is changed by the body to produce perillic acid as its primary metabolite (3). Although limonene itself is highly efficacious, perillic acid mimics the effects of limonene and can even demonstrate a stronger effect (4-6).