It was thought for years that the interstitial tissues of the brain served as a barrier to keep damaging substances from reaching the neurons of the brain and the cerebrospinal fluid. Instead of a barrier, it would be more accurate to consider it as a filter through which only molecules of a certain size or smaller can pass.

Most of the molecules of the substances used in chemotherapy are too large to pass through the blood-brain filter. Doctors don't know for sure, but it seems that in order to cross the blood-brain barrier, only molecules less than 800-1000 atomic mass units (amu) in molecular weight can get through.

In fact, when it comes to essential oils, small molecules (less than 500 amu) are what they are made of. That is why they are aromatic. The only way for something to be aromatic is for the molecules to be so small that they readily leap into the air so they can enter our noses and be detected as odor and smell.

Essential oils of every species cross the blood-brain barrier.

This makes them uniquely able to address disease, not only from a physical level, but from a more basic and fundamental level-that of the emotions which are often the root cause of physical illness.


Because of the tiny molecular structure of the components of an essential oil, they are extremely concentrated. One drop contains approximately 40 million-trillion molecules.Numerically that is a 4 with 19 zeros after it: 40,000,000,000,000,000,000. We have 100 trillion cells in our bodies, and that's a lot. But one drop of essential oil contains enough molecules to cover every cell in our bodies with 40,000 molecules.

Considering that it only takes one molecule of the right kind to open a receptor site and communicate with the DNA to alter cellular function (yes, bacteria talk), you can see why even inhaling a small amount of oil vapor can have profound effects on the body, brain, and emotions. Sometimes too many oil molecules overload the receptor sites, and they freeze up without responding at all, when a smaller amount would have been just right. This is why we say that when using oils, "sometimes less is better." Sometimes more is better, too. Knowing the difference is the art of aromatherapy.

So there you have it in a nutshell: The way the blood-brain barrier works and the biochemistry of one of the ways essential oils can help achieve a healing.