An in vitro study was also carried out on the pediculocidal effect of Lippia multiflora essential oil (Oladimeji et al 2000). In this study, 0.02 mL of the oil (in various concentrations) was applied directly to the dorsal part of freshly collected head lice. Lice were observed, and the time to “knockdown effect” (cessation of movement) recorded.

This study demonstrated a concentration-dependant knockdown time from Lippia oil (time to knockdown: 2.33 min at 100% concentration cf. 21.95 min at 10% concentration). Knockdown time was reduced if the test system was covered immediately after application of the oil (closed system), allowing build-up of oil vapour. However, the significance of this is unknown, since the study report does not indicate % mortality, and it is known that lice can be “knocked down” but subsequently recover.
In addition, the use of a direct application of the oil to the lice is an unusual method of exposing the lice, and does not allow comparison with other in vitro studies.

Several clinical trials have also been conducted on herbal pediculocides. A trial in Israel (Mumcuoglu et al 2002) compared the efficacy of a herbal spray containing coconut, anise and ylang ylang oils applied to the hair 3 times for 15 minutes at 5 day intervals
with a spray product containing 0.5% permethrin, 0.25% malathion and 2% piperonyl butoxide, applied twice for 10 minutes with a ten day interval. The natural remedy resulted in successful treatment in 60/70 (92.3%) children, while the conventional product was successful in 59/73 cases (92.2%).