THE BLOOD-BRAIN BARRIER
By David Stewart, Ph.D.,R.A.

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 sieve or 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, which is why doctors say that chemotherapy doesn’t work on brain cancer. Some of the smaller molecules get through, but not the whole suite of drugs intended.

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. Lipid solubility seems to be another factor which facilitates passing through the blood-brain barrier. Water soluble molecules don’t usually penetrate into brain tissue, even when very small. The molecules of essential oils are all not only small, but lipid soluble as well.

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.





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