Pennyroyal appears on Aries and Mars essential oil lists with the same regularity as rosemary, black pepper, and ginger, which creates the impression that it belongs in the same category as those oils. It does not. One of those oils has a documented history of fatal poisonings, and it is not rosemary. Understanding why pennyroyal keeps circulating through zodiac oil content despite being genuinely dangerous is the subject of this post, and the answer reveals something importa