Chemical additives fracture the molecular structure of essential oils, altering their chemical constituents, thus destroying their therapeutic properties. And, of course, the chemicals themselves may present a health risk. So to me pure, unadulterated essential oils are essential oils containing NO chemical additives. Using that standard, few essential oils sold in the world qualify. Indeed, according to an independent laboratory in California, Flora Research, MOST essential oils sold are either synthetic or adulterated with chemical additives.
Chemicals get into essential oils in several different ways.
Most commonly producers extend the oils by simply adding alcohol, propylene glycol, or acetate to the distilled essential oil. Some oil producers do not actually add chemicals to their oils. Imagine what happens to essential oils when chemicals are added to water, which is boiled into steam and then forced into plants to extract their oil. The very process of forcing chemically-treated steam into the plants fractures the molecular structure of the essential oils. It also seems impossible for an essential oil extracted through this method to avoid containing at least SOME of these chemical additives.