Betulinic acid is a pentacyclic triterpene. It has several botanical sources, but can also be chemically derived from betulin, a substance found in abundance in the outer bark of white birch trees (Betula alba). Betulinic acid has been found to selectively kill human melanoma cells while leaving healthy cells alive. For the past four decades, the incidence of melanoma has been increasing at a higher rate than any other type of cancer.