Most natural insect repellents are made with an essential oil
distilled from citronella, a tall, aromatic grass indigenous to
Southern Asia. Its pungent, lemony fragrance is pleasant to most
people but objectionable to mosquitoes. Other aromatic essential oils
commonly found in natural insect repellents include cedarwood,
lemongrass, eucalyptus, peppermint, pennyroyal, lavender, and bergamot.
These are safe when applied to the skin, but should not be taken
internally without the advice of a professional. Pennyroyal, in
particular, is highly toxic if ingested.