Hydrosols are the "other" part of the distillation. We simmer the plants to remove their volatile parts--these come over and out together, but some of them are lipophilic and some are hydrophilic, meaning some dissolve in fat; others in water. Essential oil tends to dissolve in fats--why we can make massage oils, and flavor our ice cream. Essential oils tend to not dissolve in water, although this is a bit more complicated, as some are heavier, and sink, some are lighter, and float, and some have a lot in common with water and are unsure, so they stay in a kind of solution with water and must be separated using a centrifuge, or some-such, but this is not the point. In general, essential oils separate themselves from the water; they are volatile. And so these are hydrosols: hydro, meaning water and sol, for solution. Water-solution, and there you have it. Hydrosols are gentler than essential oils, and can be easily incorporated into your skincare ritual.