Pennyroyal is the smallest of the mint family, and has some very distinctive properties. The taste and odor of pennyroyal is stronger and far more pungent than other mints, which makes it disagreeable to many people. It’s also disagreeable to insects, and pennyroyal has been used as a natural insect repellant for centuries.
The use of pennyroyal oil in products has become controversial when products using the oil were implicated in the deaths of two women. The herb is known to be toxic when taken in large doses, and skin contact with the pure oil can cause dermatitis.