Nicotine is fat-soluble and passes freely through cell membranes in the brain and body.

“nicotine is fat soluble. And now when anytime people hear the word fat, they tend to think about body fat, subcutaneous fat, or maybe they think about dietary fat. What I mean by fat soluble in the context of nicotine being fat soluble is that the cells of your body have an outer layer, so-called outer membrane. And it's made up of lipid, of fat, very particular types of lipids in fact. Nicotine has this remarkable ability to move through that fatty tissue. Not all molecules have that ability, but nicotine does. So it can move relatively freely through the brain and body and relatively freely from outside of cells, extracellular space to intracellular space.”