Reviewed: Greive KA, Barnes TM. The efficacy of Australian essential oils for the treatment of head lice infestation in children: a randomised controlled trial [published online March 7, 2017]. Australas J Dermatol.

Head lice infestation, most often seen in children aged 3 to 14 years, causes itching and discomfort, and can result in embarrassment, school absences, and parental anxiety. Traditional treatments, such as those that contain organochlorines, organophosphates, carbamates, pyrethrins, and pyrethroids, have been shown to be neurotoxic to insects. Use of these treatments has raised safety concerns because of possible adverse effects (e.g., allergic reactions, skin irritation, and sneezing) and has led to resistant lice populations. Alternative treatments have been developed for improved efficacy and to reduce concerns about potential neurotoxicity. The authors of this study conducted multiple assessments: two human clinical trials, a skin irritation and sensitization analysis, and an in vitro study. Trial 1 was a multicenter, randomized, parallel-group study that compared the safety and efficacy of a solution containing Australian eucalyptus (Eucalyptus globulus, Myrtaceae) oil and lemon-scent tea tree (Leptospermum petersonii, Myrtaceae) oil (EO/LP) to a mousse containing pyrethrins and piperonyl butoxide (P/PB) for treating head lice in children. Trial 2 was a single-blind, open-label study that assessed the efficacy of the EO/LP solution for killing head lice after a single application. Skin irritation and sensitivity tests were conducted in both adults and children, and the efficacy of the EO/LP solution for killing lice and louse eggs was tested in vitro.

Trial 1

The first study was conducted in Queensland, Australia, and included male and female schoolchildren up to grade 7 who had live head lice in their hair or on their scalp upon visual inspection and dry-combing with a head lice comb. The EO/LP treatment used was MOOV Head Lice Solution (Ego Pharmaceuticals Pty Ltd.; Braeside, Victoria, Australia), which contained 11% by weight eucalyptus oil and 1% by weight lemon-scent tea tree oil. The P/PB treatment was Banlice Mousse (Pfizer Consumer Healthcare Group; West Ryde, New South Wales, Australia), which contained 1.65 mg of pyrethrin and 16.5 mg of piperonyl butoxide per gram of mousse. 

The EO/LP solution was applied three times (on days 0, 7, and 14). Although the P/PB mousse manufacturer recommended only one treatment, the mousse was applied twice (on days 0 and 7), as recommended by the Therapeutic Goods Administration of Australia. The technicians applying the treatments were not blinded because of the differences in odor and appearance between the treatments. However, the assessment technicians, subjects, and parents did not know which treatment was being used.

The intention-to-treat (ITT) population, which included all randomly assigned subjects before treatment, was used to determine the safety and efficacy of the two treatments. The per-protocol (PP) population included subjects who completed all treatments of the EO/LP solution or the P/PB mousse. Subjects’ siblings who had lice were enrolled in the trial and treated in the same manner. Siblings with no head lice but with evidence of recent infestation underwent wet-combing. Any adverse effects were recorded at each study visit.

Of the 97 subjects in the ITT population, 76 met the requirements for the PP analysis. Subjects did not meet the PP requirements for the following reasons: one did not receive the required dose, three used alternative head lice treatments during the trial, 15 failed to comply with sibling control criteria, one failed to appear on day 21, and one withdrew due to an adverse event. Of the PP population, 40 received the EO/LP solution and 36 received the P/PB mousse.

Analysis of the PP population revealed a significant between-group difference in cure rate when measured seven days after the last application (i.e., on day 14 for the P/PB group and on day 21 for the EO/LP group). At that time, 83% of the EO/LP group and 36% of the P/PB group were cured (P < .0001). On day 1, there was no significant difference in cure rate between the two groups. In the ITT subjects, seven days after the last application, 71% of the EO/LP group and 33% of the P/PB group were cured (P = .0002). No significant between-group difference in cure rate was observed on day 1. 

Of the 97 subjects who received at least one treatment, 21 adverse effects were reported in 13 subjects. The 18 adverse effects reported in the EO/LP group included transient mild-to-moderate sensations, such as itchiness, stinging, or burning that lasted no more than five minutes and required no treatment. The three adverse effects in the P/PB group included one crawling sensation and two stinging sensations.

Trial 2

In the second trial, 11 subjects with live lice received treatment with the EO/LP solution on day 0. The authors report that after the single EO/LP application, all of the 1,418 head lice collected from the children were considered dead as they were wet-combed out of the hair. Upon repeat examination 30 minutes after combing, all lice were confirmed dead. 

Skin Irritation and Sensitivity Study

The skin irritation and sensitivity study included separate groups of both adults and children. Fifty-three of the 56 adult subjects (aged 28 to 74 years) enrolled in this study completed it. The three who withdrew from the study did so for reasons unrelated to the study protocol. A patch containing the EO/LP solution was applied to the skin of the back for 24 hours every Monday, Wednesday, and Friday for three consecutive weeks. Then, 10 to 14 days after the last application, a “challenge or retest dose” was applied to a previously unexposed test site on the skin of each subject and assessed 24 and 48 hours later. The authors observed no erythema (reddening of the skin), edema (inflammation of the skin), or adverse effects. 

For the pediatric testing of skin irritation and sensitivity, the EO/LP solution was applied to the scalp, face, and neck of 20 children (aged six months to four years) on days 0, 7, and 14. The subjects were evaluated after each application and again 24 hours after the last application. The authors observed no test-related irritation, and the subjects (and their parents or guardians) made no “safety-related comments.”

In Vitro Assessments

As part of the in vitro component of the study, the authors immersed louse eggs in the EO/LP solution and a control solution (purified water). The authors observed that no louse eggs hatched for 10 days after a 10-second immersion in the EO/LP solution. Following immersion in the control solution, 92% of the louse eggs had hatched after 10 days.

In another in vitro analysis, the authors submerged live body lice in the EO/LP solution and control solution for 10 minutes. Sixty minutes after immersion, the authors observed that 100% of the body lice in the EO/LP solution were moribund or dead. All of the body lice immersed in water were alive after 60 minutes.

Conclusion

In trial 1, the authors attribute the treatment failures seen in seven of the 40 subjects (17.5%) in the EO/LP group to the fact that lice or eggs had survived any one of the three treatments or that re-infestation had occurred. (For comparison, treatment failures were seen in 23 of the 36 subjects [63.9%] in the P/PB group.)

The authors conclude that “the EO/LP solution contains a proprietary combination of essential oils that has been shown to be safe and effective in eliminating head lice in Australia.” In addition, they suggest that head lice may be less likely to develop resistance to the EO/LP solution compared to the P/PB solution. “The resistance of head lice to neurotoxic treatments is thought to develop when there is an incomplete kill, or when low levels of therapeutic agents remain on the scalp,” the authors explain. Because the solution is both volatile and quickly effective, “it is unlikely to cause the development of head lice resistance in the community.”

—Shari Henson