The active antifungal substance present in Cinnamon Oil is Eugenol ( the same in Clove Oil ) you have to be very careful if someone is planning on ingesting it because it is very toxic to the liver. I haven’t found any paper documenting how safe it is when taken orally. If you find one, please share.
I know about Eugenol since long time but never used it because its toxicity. Eugenol is a very powerful antifungal probably stronger than Carvacrol.