Now I think about it, mucous membranes don't all have the same degree of sensitivity. You don't need to be as careful about what goes on your lips as what goes in your vagina, and you definitely need to be a lot more careful about putting things in your eyes. I've had irritation problems from a lipbalm which had cinnamon oil in it, and had to stop using it. It's a known problem with that particular lip balm (a Hurraw one). Quality and adulteration is a big problem with essential oils, and it's rare to find vanilla sold as an essential oil rather than a food extract or fragrance oil. Many people find that they have to avoid additives such as fragrance in lubricants, and lubricants which offer extra features such as "flavoured", "tingling" or "warming" are notorious for causing all sorts of problems. Tea tree is actually quite popular for treating yeast infections, but it has to be suitably diluted, and even so may cause irritation. There are also potential problems with ingesting essential oils, so you'd certainly need to keep the dilution low for that reason. My advice would be to do unscented suppositories or lube as standard, look carefully into which essential oils have a good reputation for vaginal use, and if offering them as an extra, warn that they may cause irritation and state the dilution used. As someone who's fond of essential oils and has used them on and off for decades, I'm curious as to how the fragrances would combine. Vetiver, perhaps? Meanwhile, a kind person has supplied me with some suppositories! More on the thread I started about my own medical issues.