Although it is apparently unacceptable to state this (article to Journal rejected), Gentian/crystal violet, a naturally occurring aniline dye, was for many years an incredibly effective treatment for foot and leg ulceration.
I have done a lot of research into why it is no longer acceptable, and all I can find (apart from a few local reactions, which happen in all drugs), is a research project in which rats were fed on food containing the dye over a period of months. Some of the rats contracted gastric cancer.
In podiatry, the usage is minute, a spot of dye on an inter digital corn will produce amazingly quick healing.
As a case history, a very overweight patient, who does not take responsibility for his health came for podiatry treatment. He had two 10p sized ulcers on his ankle. I advised him to go to the practice nurse for treatment. He was travelling abroad the next day. "isn't there something I could use" he said.
Knowing him well, I felt bound to suggest Gentian violet. He procured some from the internet.
When he returned to me three months later, the ulcers were completely healed.
It is clearly not in the interests of some large organisations for very cheap treatments such as this to be used, when very expensive single package drugs and dressings create enormous profits...