A methylanthraquinone derivative of aloe-emodin, it is known for effective treatment of chronic diseases of the skin such as psoriasis and trichophytosis (a skin fungus). On its own it exhibits certain high levels of toxicity. In the context of Aloe Vera gel, no such toxicity is measureable.
ref: Silent Healer (pg. 51) by Bill Coats R.Ph., with Robert Ahola