Because when applied to skin..cells..it kills cells and a scab forms. Scabs are eschars.
The concentrated salves, tinctures, etc. are the ones to be most concerned about as far using externally or internally.
It is poisonous and if used must be used with great care and knowledge.
Those salves are doing that, aren't they? Killing cells...'burning'...Being promoted and sold as cancer cures.
This is another herb, natural remedy that should not be taken without an expert.
Please, People....do some research independent of those that are trying to sell something.