Both the layman and specialist must be knowledgeable about it. If the preceding actions were forbidden by Allah and His Messenger to the fasting person because they would ruin the fast, then it would have been obligatory upon the Messenger to clarify that fact. If he had done so, his companions would have known about it and would have passed it on to the rest of the Muslims. It is well-known that kohl was in common use as were oils, washing, incense, and perfume. Since he did not do so, they belong to the class of perfumes, incense, and dyes.
Incense goes through the nose and enters the head and lands on the body.
Dyes or oils are absorbed by the skin and the body is refreshened by it. The case of perfumes is similar. The Muslims during the time of the Prophet would injure themselves, either from jihad or otherwise, and would injure their stomachs or skulls. Anal enemas are also not taken as food. Indeed, it helps the body to release whatever is in the intestines and it does not reach the stomach.