At toxic doses, any substance, including essential oils, can be damaging to the body—damage that begins at the cellular level. If too many cells become affected, damage of entire tissues or organs may result.

One of the primary ways that substances cause cellular damage is by disrupting the cell’s membrane. Recall from Module 2 that a cellular membrane is the outer most boundary of a cell that separates its internal contents from the environment. In order to provide this separation, cellular membranes are composed of a special phospholipid bilayer. A phospholipid is a type of lipid molecule containing a hydrophilic head and two hydrophobic tails. A bilayer simply means that the membrane is composed of two layers of phospholipids that are lined up tail-to-tail to form a continuous, waterproof barrier. This barrier is important for the life of the cell because it keeps vital molecules and organelles inside of the cell, while simultaneously preventing unwanted substances from entering the cell.


However, essential oils are lipid soluble, so they easily penetrate the membrane and are able to enter a cell’s internal environment. Although beneficial at appropriate doses, at toxic doses, essential oils can overwhelm the cell and cause damage to the membrane. When this occurs, the cell cannot maintain its delicate equilibrium and molecules or fluid are able to enter or exit the cell uncontrollably. As a result, the cell loses its ability to function normally and dies. If membrane damage occurs in a large number of cells, it may disrupt the functionality of the whole organ or tissue.

Another way a toxic dose of a substance may harm cells is by damaging their organelles. Mitochondria, the organelles responsible for energy production, are especially susceptible. When mitochondria become damaged, their energy production abilities are impeded, which in turn prevents the cell from thriving. Malfunctioning metabolism can even further aggravate the problem by producing unusually high levels of oxidizing agents. If these agents are sent out of the cell, they can damage other healthy cells, further compounding the problem. There are many other ways that a toxic dose of something can cause cytotoxicity, including interfering with normal cellular metabolism, blocking chemical reactions, interrupting signaling pathways, fragmenting DNA, or inducing apoptosis. The mechanisms of action by which essential oils cause cytotoxicity are being widely studied and vary oil by oil. Further investigation and clinical trials are needed to more fully understand these processes.

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