Pennyroyal oil is a strong insect repellent and is often
used by herbalists as such on leather soaked dog collars. It can be strong and irritating for sensitive skin however.
A word of caution on the use of pennyroyal oil for any internal use some misinformed herbal advisers have suggested its use as an abortifacient, and it has been used in Colorado for this purpose. Several fatal accidents have occurred as a result of its use. Do NOT use it internally!