In vitro comparison of four treatments which discourage infestation by head lice

Head lice are attracted to their hosts via a number of factors including humidity, temperature, and a combination of body odours and chemicals (Mumcuoglu et al. 1996, 2004). Head lice are very particular in regards to selecting a new host and will only transfer hosts when conditions are optimal (Canyon et al. 2002). An effective product would benefit a potential host by altering their scalp environment thereby making conditions suboptimal for head lice. Under such conditions head lice are less likely to commit to a host transfer.

Head lice are yet to be successfully colonized. Human body lice as opposed to head lice were studied in these experiments. Body lice can be kept alive in the laboratory for long periods of time by feeding them on rabbits which cannot be done for head lice, who will only feed off humans. While it is well recognised that there are distinct morphological differences between human head lice and body lice, it has been demonstrated using mDNA that they are conspecific, that is they represent the one species (Leo et al. 2002). Therefore the use of human body lice as a surrogate for human head lice is not unreasonable.

A challenge test using filter paper in a closed petri dish rather than hair on a human head was used to test the four products since it gives the lice two choices only: a surface with test product or without test product. If we had used hair covered in test product in a petri dish to determine if lice wanted to be on the hair or off the hair, the lice may not have gone on the hair by chance rather than choice given the limited surface area of hair compared with the petri dish. Lice like the dark, so they could have used the shade of the treated hair to escape the light when the petri dish was brought out for inspection. A recent study has demonstrated the difficulties of testing this type of product on hair compared with paper (Semmler et al. 2011). In this study, lice were placed on horizontal treated hair hung up vertically so that they would have a chance to let themselves drop down onto the soil. However, they decided to stay and crawl upwards apparently “hoping” to reach “better smelling” regions of the hair (Semmler et al. 2011).

MOOV Head Lice Defence Spray was found to be significantly more effective at discouraging the transmission of body lice than the water control, Wild Child Nits Head Lice Defence Spray, 100% Natural Headlice Beater, and Lysout Natural Anti-Lice Spray for up to 8 h. MOOV Head Lice Defence Spray leaves a residue on hair once the alcohol from the product rapidly evaporates consisting of diisopropyl adipate, trimethylpentanediol/adipic acid/glycerin crosspolymer and tocopherol. Head lice find this residue “dirty” and unattractive and thus are discouraged from infesting hair which has been treated with this product. The ingredients in the residue, individually or in combination, do not have any known repellency action like that shown for diethyltoluamide (DEET).

With the increasing global prevalence of pediculosis, the number of products claiming to discourage the transmission of head lice available over the counter has increased dramatically. However, the effects associated with these products are only presumed, and very few studies on the efficacy of products to discourage head lice transmission have been published. For example, in vitro studies have found that essential oils such as rosemary (Mumcuoglu et al. 1996), lavender (Burgess 1993a), piperonal (Burgess 1993b; Peock and Maunder 1993), eucalyptus (Mumcuoglu et al. 1996; Toloza et al. 2006, 2008) and citronella (Mumcuoglu et al. 1996) are promising candidates as compounds which discourage the transmission of head lice; however, formulation into suitable products for commercial use has not been studied. Components of some essential oils such as 1,8-cineole (Toloza et al. 2008), anisole (Toloza et al. 2006; 2008) and chavibetol (Bagavan et al. 2011) have also been shown to be possible candidates. One in vitro study found that several commercially available products including DEET did not show sufficient efficacy to discourage head lice transmission to be endorsed (Canyon and Speare 2007). Another in vitro study found that DEET, icaridin, and IR 3535 only discouraged head lice for 2 h when applied to hair, while three commercial products, Linicin Preventive Spray (Semmler et al. 2011) formerly named Licatack Preventive Spray (Semmler et al. 2010, 2011) containing paramenthandiol (PMD) and an extract of the Vitex agnus-castus plant, as well as Picksan NoLice containing PMD and a neem seed extract (Semmler et al. 2011), discouraged head lice for a prolonged period of time. In the only clinical trial published to date, a slow release citronella formulation was found to be safe and effective at discouraging head lice transmission in children (Mumcuoglu et al. 2004).

This study has shown that out of the four head lice repellents tested, MOOV Head Lice Defence Spray offers the best efficacy and consistency of performance. Use of an effective product which discourages the transmission of head lice could significantly lower the incidence of reinfestation, which among other beneficial effects would lower expenditure on head lice control and the time spent on treatment and removal of lice. No less important would be the psychological and social benefits gained by eliminating the stigma and social isolation associated with louse infestation.