Essential oils have been used for thousands of years. The Ancient Egyptians were well-known to use them both both medicinally and also for aroma therapy. They were also used extensively in India as part of Ayurvedic medicine. And of course botanical medicines were used by many peoples around the world for generations. Hippocrates, considered the father of modern medicine, documented the medicinal properties of over 300 plants.
And, of course, the food-grade oils can also be used as food flavouring, which becomes particularly useful when avoiding sugar and other nasties.
My favourite use for essential oil is orange oil in chocolate. Orange chocolate was one of my favourites growing up, but I am unaware of any healthy versions. So I made my own, which is available in my Easy Keto cookbook.
I initially had trouble locating a good orange oil for cooking, so here is a link to Australian Essential Oils, who make a beautiful sweet orange oil.
Sendra, E., 2016. Essential oils in foods: From ancient times to the 21st century.