Essential oils of aniseed, cinnamon leaf, red thyme, tea tree, peppermint, nutmeg, rosemary,
and pine were tested in vitro against lice, Pediculus humanus. All the oils except for rosemary
and pine were found to be effective in the laboratory when applied in an alcoholic solution
and followed by a rinse the following morning in an essential oil/vinegar/water mixture.
Peppermint and nutmeg were only used as a blend rather than as individual oils. Problems of
solubility and toxicity are discussed, as are possible mechanisms of action. Phenols, phenolic
ethers, ketones, and oxides (I, 8-cineole) appear to be the major toxic components of these
essential oils when used on lice. Aldehydes and sesquiterpenes may also play a role.