Yes and no! It depends on what kind of essential oil!
As a rule of thumb, pure essential oils that have GRAS (Generally Recognized as Safe) can be ingested. You can find GRAS essential oils by searching GRAS on our website, or by clicking this link. However there are maximum oral doses, and for this you have to consult a certified aromatherapist or buy a book about essential oil safety. However, if it's used only as a flavoring, then it should be fine. Note that essential oils are very powerful. Most of the time, you only need a drop to flavor your food. For maximum flavoring effect, add at the end of cooking (just like cooking with fresh herbs) or you lose the flavor.
Regarding purity, essential oils can be adulterated so it can be cheaper. Try to get organic essential oils as well to make there are no pesticides and other nasties.
Why do we put in our disclaimer that we do not recommend ingesting essential oils - this is because if used improperly, it can be fatal! Unless you know exactly what you are doing, please do not ingest without an aromatherapist's recommendation. This is also the reason why our essential oils are packed in bottles with childproof cap.
If you have any questions, feel free to email us at firstname.lastname@example.org