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ORIGINAL RESEARCH
The efficacy of Australian essential oils for the treatment
of head lice infestation in children: A randomised
controlled trial
Kerryn A Greive and Tanya M Barnes
Ego Pharmaceuticals, Braeside, Victoria, Australia
ABSTRACT
Background: The increase in resistance of head
lice to neurotoxic pediculicides and public concern
over their safety has led to an increase in alternative
treatments, many of which are poorly researched or
even untested.
Methods: A multicentre, randomised, assessor-
blind, parallel-group trial (Trial 1) was conducted to
compare the safety and efficacy of a head lice treat-
ment containing Australian eucalyptus oil and Lep-
tospermum petersonii (EO/LP solution; applied thrice
with 7-day intervals between applications) with a
neurotoxic treatment containing pyrethrins and
piperonyl butoxide (P/PB mousse; applied twice with
a 7-day interval) in children. A single-blind, open trial
(Trial 2) was conducted to assess the efficacy of EO/
LP solution following a single application. In addition,
skin irritancy and sensitisation tests using EO/LP
solution were performed in adults and children.In
vitro tests were performed to further assess the ovici-
dal and pediculicidal efficacy of EO/LP solution.
Results: EO/LP solution was found to be more than
twice as effective in curing head lice infestation as
P/PB mousse in per-protocol participants (Trial 1;
83% vs 36%, P<0.0001), and was also found to be
100% pediculicidal following a single application
(Trial 2). Adverse events were limited to transient
itching, burning or stinging. Further skin testing
with the EO/LP solution reported no irritation or
sensitisation in adults, or irritation in children. In
vitro exposure of lice and eggs to the EO/LP solution
resulted in 100% mortality.
Conclusion: The efficacy, safety and relative ease
of use of the EO/LP solution make it a viable alter-
native in treating head lice.
Key words: eucalyptus oil, head lice, lemon tea
tree oil, piperonyl butoxide, pyrethrin, resistance.
INTRODUCTION
Infestation with head lice is one of the most common para-
sitic infestations of humans worldwide.
1
Schoolchildren
aged between 3 and 14 years are generally the most
affected group, with the prevalence of lice infestation esti-
mated to be between 6–12 million children in the USA
annually.
2
The main symptoms associated with infestation
include itching and discomfort, which may lead to substan-
tial social distress, parental anxiety, embarrassment, and
unnecessary absence from school and work.
3
The cost of
head louse infestation in the USA has been estimated to be
$1 billion annually.
4
Traditional head lice treatments include a wide variety
of neurotoxins including organochlorines (lindane),
organophosphates (malathion), carbamates (carbaryl), pyr-
ethrins and pyrethroids (permethrin, D-phenothrin).
1
How-
ever, this arsenal of pediculicides has failed to obtain
adequate control.
5
Moreover, their repeated use, residual
nature and misapplication has led to the selection of resis-
tant populations of lice in Australia
6
and worldwide.
7–11
The increasingly poor performance of neurotoxic head
lice treatments and the growing public concern over their
use has led to an increase in the commercialisation of
alternative treatments.
12
Plant essential oils and their con-
stituents provide a rich source of bioactive chemicals that
Abbreviations:
EO/LP eucalyptus oil and Leptospermum petersonii
ITT intention-to-treat
P/PB pyrethrins and piperonyl butoxide
PP per-protocol
Correspondence: Dr Kerryn A Greive, Ego Pharmaceuticals Pty
Ltd, 21–31 Malcolm Road, Braeside, Vic. 3195, Australia. Email:
kerryng@egopharm.com
Kerryn A Greive, PhD. Tanya M Barnes, PhD.
Conflict of interest: Kerryn Greive and Tanya Barnes are
employed by Ego Pharmaceuticals, the sponsor of the study and
manufacturer of MOOV Head Lice Solution.
Submitted 5 September 2016; accepted 30 December 2016.
Australasian Journal of Dermatology (2017) ,– doi: 10.1111/ajd.12626
©2017 Ego Pharmaceuticals Pty Ltd. Australasian Journal of Dermatology published by John Wiley & Sons, Ltd. on behalf of The
Australasian College of Dermatologists.
This is an openaccess article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properlycited.
are easily extractable and biodegradable and generally
have low mammalian toxicity.
13–15
However, very few
in vitro and clinical studies have evaluated the effective-
ness of these alternative compounds, and the bulk remain
to be scientifically tested.
16
The aim of this study was to compare the safety and effi-
cacy of a head lice treatment containing Australian euca-
lyptus oil and Leptospermum petersonii (EO/LP) with a
neurotoxic treatment containing pyrethrins and piperonyl
butoxide (P/PB) in children (Trial 1). The efficacy of the
EO/LP solution in killing head lice after a single applica-
tion was also examined (Trial 2). To rigorously assess the
safety of the EO/LP solution, additional skin irritancy and
sensitisation tests were performed in both adults and chil-
dren. The ovicidal and pediculicidal efficacy of EO/LP
solution was also tested in vitro to eliminate the confound-
ing effect of reinfestation.
METHODS
Ethics statement
All trial activities were approved by the Human Research
Ethics Committee of the University of Queensland. The
study was entered in the Australian/New Zealand Clinical
Trial Registry: registration no. NCT00381082.
Participants
Eligible participants were male and female Queensland
primary school children (up to Year 7) with live head lice
(adults or nymphs), not just eggs, on the hair or scalp, as
determined by visual inspection and dry-combing of hair
with a head lice comb. The combing stopped immediately
when live lice were detected. Further inclusion criteria
were: participants were available for the trial duration;
were willing to abstain from using any other lice treat-
ments, including head lice combs, for the duration of the
trial; written informed consent given by their parent or
guardian. The exclusion criteria were: a history of aller-
gies to head lice products or the specific components being
tested; treatment for lice in the 4 weeks prior to commen-
cing the trial; and the presence of scalp disease. Further, if
a participant had primary school-aged siblings, those
siblings were screened and enrolled in the trial if they had
head lice.
Interventions
MOOV Head Lice Solution (Ego Pharmaceuticals, Braeside,
Victoria, Australia) containing 11% w/w eucalyptus oil and
1% w/w Leptospermum petersonii (EO/LP) and Banlice
Mousse (Pfizer Consumer Healthcare Group, West Ryde,
New South Wales, Australia) containing 1.65 mg/g pyre-
thrins and 16.5 mg/g piperonyl butoxide (P/PB). The P/PB
mousse was chosen as the neurotoxic comparator for this
study as it is a market leader in Australia.
Trial 1: Efficacy and safety of the EO/LP solution
compared to the P/PB mousse
A schematic representation of the trial design is shown in
Table 1. After informed consent was obtained, participants
meeting the inclusion criteria were identified, randomised
and assigned to receive one of the two lice treatments.
The EO/LP solution was applied thrice with a week
between applications, as per the manufacturers’instruc-
tions, i.e. at day 0, day 7 and day 14. As head lice eggs can
take up to 10 days to hatch, the use of three applications
was designed to ensure that any lice hatching from eggs
laid immediately before the first application would be
killed by the third application. Although the P/PB mousse
claimed that only one treatment was required to effect a
cure, it was applied twice using the manufacturers’
instructions, with a week between applications, i.e. at day
0 and day 7, which is in accordance with the recommenda-
tions of the Therapeutic Goods Administration of Aus-
tralia.
17
Given the physical differences and differences in smell
between treatments, the technicians applying the treat-
ments could not be blinded, but effective blinding of the
assessment technicians was achieved by the physical sepa-
ration of the application and assessment staff and by docu-
ment control procedures. Participants and parents were
also prevented from sighting the treatment used.
During the trial participants were free to wash their hair
with ordinary shampoo and conditioner and to comb with
Table 1 Schematic representation of Trial 1 designed to compare the safety and efficacy of the EO/LP solution to the P/PB mousse in a
multicentre, randomized, assessor-blind, parallel-group trial
Day 0 Day 1 Day 7 Day 14 Day 21
Informed consent All ––– –
Hair/scalp examination by dry-combing
(combing stopped once live head lice observed)
All All –– –
Inclusion/exclusion criteria All ––– –
Randomisation All ––– –
Treatment with EO/LP solution or P/PB mousse All All EO/LP solution group ONLY –
Hair/scalp examination by wet-combing
(combing stopped once live head lice observed)
–––P/PB mousse group ONLY EO/LP solution group only
Adverse events All All All All subjects EO/LP solution group only
EO/LP, eucalyptus oil and Leptospermum petersonii; P/PB, pyrethrins and piperonyl butoxide.
2 KA Greive and TM Barnes
©2017 Ego Pharmaceuticals Pty Ltd. Australasian Journal of Dermatology published by John Wiley & Sons, Ltd. on behalf of The
Australasian College of Dermatologists.
standard combs. Participants were free to withdraw from
the trial at any time.
Per-protocol (PP) assessment
The intention-to-treat (ITT) population was defined as all
participants post-randomisation and before treatment com-
menced. The ITT population was the primary population
used for the determination of safety and efficacy. To be
considered PP, the participant must have received three
treatments of the EO/LP solution or two treatments of the
P/PB mousse, each 7 days apart.
In addition, the hair of siblings in grades 1–7 of the
enrolled participants was examined. If found to be infected
with head lice, this sibling was treated with the same head
lice product as the enrolled participant on day 0 and was
enrolled in the trial. If the sibling was found not to have
live head lice but showed evidence of recent infestation
(live or dead eggs), the sibling was wet-combed out. If the
sibling had no live lice, live or dead eggs, no further treat-
ment was undertaken.
Efficacy assessment
The primary efficacy end-point was the cure rate 7 days
after the last application, i.e. day 14 for the P/PB mousse
and day 21 for the EO/LP solution. A cure is defined as the
absence of live lice, adults or nymphs, as diagnosed by
wet-combing. Wet-combing is considered the best tech-
nique for diagnosing head lice infestation.
18,19
For this
study the wet-comb technique was standardised and car-
ried out by trained technicians. The secondary efficacy
end-point was the cure rate at day 1 for both products,
defined as the complete absence of live lice as diagnosed
by visual inspection and dry-combing.
Safety assessment
The ITT population was used for the safety evaluation.
The incidence and severity of adverse events was recorded
at each visit.
Trial 2: Efficacy after a single application of the
EO/LP solution
A schematic representation of the trial design is shown in
Table 2. Participants’characteristics and the inclusion and
exclusion criteria were the same as for Trial 1. During the
treatment application, the participants’eyes were covered
and they were unaware of the product being applied.
The EO/LP solution was applied once according to the
manufacturer’s instructions. Hair was washed, partly dried
and non-medicated hair conditioner massaged through,
particularly near the scalp. The conditioned hair was
divided into sections and wet-combed. Each section of hair
was combed six times or until no more lice were detected.
Each combing was collected on a tissue. If lice were pre-
sent they were visually inspected for any movement,
blotted to remove conditioner, and the essential oils were
allowed to evaporate.
The head lice were left to recover and carefully assessed
using a method adapted from Speare
15
30 min after comb-
ing was complete using a magnifying lens and probe as
being either alive: able to move and right itself when
rolled onto its back; moribund: cannot right itself when
rolled onto its back; or dead: no movement of any kind.
This time point was chosen since preliminary studies of up
to 24 h revealed that if lice were moribund after 20 min,
they were significantly incapacitated and death was immi-
nent. The primary efficacy end-point was the number of
children from whom head lice showed no signs of life
(neither alive nor moribund) 30 min after combing out.
Skin irritancy and sensitisation study
The safety of the EO/LP solution was patch tested as previ-
ously described.
20
Briefly, the EO/LP solution (0.2 mL) was
dispensed onto a patch which was affixed directly to the
skin of the back and left in place for 24 h. This procedure
was repeated every Monday, Wednesday and Friday for 3
consecutive weeks, for a total of nine consecutive 24-h
exposures. In the event of an adverse reaction, the area of
erythema and oedema was measured prior to the next
patch application.
Participants were given a 10 to 14-day rest period after
which a single challenge or retest dose was applied to a
previously unexposed test site, which was assessed 24 and
48 h after application.
Paediatric testing
All participants were examined (scalp, face and neck) on
day 1 of the single-blind study by a paediatrician and
enrolled if they met the entry criteria. Inclusion criteria
were: pre-pubescent children; written informed consent
given by their parent or guardian. Exclusion criteria were:
taking medication likely to interfere with the test, includ-
ing steroidal and non-steroidal anti-inflammatory drugs or
antihistamines; enrolled in other tests; known hypersensi-
tivity to soaps, detergents, fragrances or shampoos;
Table 2 Schematic representation of Trial 2 designed to assess
the efficacy of EO/LP solution following a single application in a
single-blind, open trial
Performed for all subjects at Day 0
Informed consent
Hair/scalp examination by dry-combing (combing stopped once
live head lice observed)
Inclusion/exclusion criteria
Treatment with the EO/LP solution
Hair/scalp wet-combed until no more head lice observed. Head
lice collected
Head lice observed 30 min post collection and assessed as alive,
moribund or dead
EO/LP, eucalyptus oil and Leptospermum petersonii.
Australian essential oils for head lice 3
©2017 Ego Pharmaceuticals Pty Ltd. Australasian Journal of Dermatology published by John Wiley & Sons, Ltd. on behalf of The
Australasian College of Dermatologists.
dermatological or pre-existing conditions likely to interfere
with the test.
The EO/LP solution was applied by a trained technician
according to the manufacturer’s instructions at days 0, 7
and 14. At each time point, the participants were evalu-
ated for irritation using the following scale: 0 =no irrita-
tion present; +=barely perceptible irritation present;
1=slight irritation present; 2 =mild irritation present;
3=moderate irritation present and 4 =severe irritation
present. Any additional dermatological finding (rash, skin
dryness) to the contact areas (scalp, face and neck) was
noted. If any irritation reactions were noted, an additional
evaluation of the chest, back and abdomen was per-
formed.
All parents or guardians were instructed to report any
adverse experiences or concerns related to the use of the
EO/LP solution. Participants were evaluated again 24 h
after the last application.
In vitro ovicidal and pediculicidal efficacy
For the in vitro tests, human body lice (Pediculus humanus
var humanus) as opposed to head lice were studied, as
they can be kept alive in the laboratory for long periods of
time by feeding them on rabbits. This is extraordinarily
difficult for head lice, which will feed off humans only.
While it is well recognised that there are distinct morpho-
logical differences between human head lice and body lice,
it has been demonstrated using mitochondrial DNA that
they are conspecific, that is, they represent the one spe-
cies.
21,22
Therefore, the use of human body lice as a surro-
gate for human head lice is not unreasonable.
The in vitro ovicidal and pediculicidal efficacy of the
EO/LP solution was determined as previously
described.
20,23
Briefly, eggs and body lice were exposed to
the EO/LP solution for 10 s. Purified water was used as the
control. The number of eggs that hatched was recorded
after 6, 7, 8, 9 and 10 days. Five replicates of 20 eggs each
was performed, giving a total of 100 eggs per group. The
results from the replicates were pooled, with the data pre-
sented as the total percentage of hatched eggs.
The body lice were observed for 60 min following expo-
sure and classed as alive, moribund or dead according to
the definitions adapted from Speare’s method
15
described
above. Four replicates of 25 body lice each were performed
for the EO/LP solution, giving 100 lice. Two replicates of
25 body lice each were performed for the water control,
giving 50 body lice. The results are given as % corrected
mortality calculated as follows: corrected mortality =([%
alive in water control—% alive in test]/% alive in water
control) 9100.
Statistics
Based on previous studies, the cure rate among children
treated with the EO/LP solution and the P/PB mousse was
expected to be approximately 70 and 30%, respectively. It
was estimated that 29 participants were required in each
group in order to show a statistically significant difference
between both groups with 80% power and an overall level
of significance of P=0.05. Sufficient participants were
enrolled to ensure that a minimum of 29 PP participants
per treatment arm completed the protocol.
For trial results, v
2
tests with a Bonferroni adjustment
were used to compare the treatment groups at each time
point, day 1 (secondary efficacy end-point) and day 14 (pri-
mary efficacy end-point for the P/PB)/day 21 (primary effi-
cacy end-point for the EO/LP). The analysis was
performed for the ITT and PP populations. For the in vitro
studies, statistical analysis was performed using the
unpaired Student’st-test at a significance level of 5%.
RESULTS
Trial 1: Efficacy and safety
The participants’characteristics showed no significant dif-
ferences between treatment groups in relation to sex,
school attended, grade, or hair length (data not shown). Of
the 97 children in the ITT population, 76 complied with all
aspects of the protocol and were considered PP. Of the PP
population, 40 received the EO/LP solution and 36
received the P/PB mousse. Reasons for a participant being
deemed not PP were: they did not receive the required
dose (1 vs 0 for the EO/LP solution and P/PB mousse,
respectively); they used alternative head lice treatments
during the trial (1 vs 2); they failed to comply with sibling
control criteria (5 vs 10); they failed to appear for assess-
ment at day 21 (1 vs 0). One participant treated with the
EO/LP solution withdrew from the trial due to an adverse
event.
Table 3 shows the analysis for PP participants. A signifi-
cant difference was found in the number of participants
cured in the EO/LP group (83%) compared with the P/PB
group (36%; P<0.0001) for the primary efficacy end-point.
No statistically significant difference was found between
the EO/LP group (60%) and the P/PB group (47%;
P=0.2645) for the secondary efficacy end-point.
Table 4 shows the analysis for ITT participants. A signif-
icant difference was found in the number of participants
cured in the EO/LP group (71%) compared with the P/PB
group (33%; P=0.0002) for the primary efficacy end-point.
No statistically significant difference was found between
the EO/LP group (55%) and the P/PB group (40%;
P=0.1259) for the secondary efficacy end-point.
Table 3 Trial 1: Cure rates for the primary and secondary effi-
cacy end-points for per-protocol participants
Treatment
Primary end-point
†
n/n,%
Secondary
end-point
‡
n/n,%
EO/LP solution 33/40 (83) 24/40 (60)
P/PB mousse 13/36 (36) 17/36 (47)
Pvalue <0.0001 0.2645
†
Cure rate 7 days after the last application, i.e. day 14 for P/PB
mousse and day 21 for EO/LP solution.
‡
Cure rate at day 1 for both
products as diagnosed by visual inspection and dry-combing of the
hair and scalp. EO/LP, eucalyptus oil and Leptospermum petersoni;
P/PB mousse, pyrethrins and piperonyl butoxide.
4 KA Greive and TM Barnes
©2017 Ego Pharmaceuticals Pty Ltd. Australasian Journal of Dermatology published by John Wiley & Sons, Ltd. on behalf of The
Australasian College of Dermatologists.
Of the 97 participants who received at least one treat-
ment, 21 adverse events were reported in 13 participants;
18 in the EO/LP group (mainly transient mild to moderate
sensations described as either itchiness, stinging or burn-
ing lasting no more than 5 min and requiring no treat-
ment) and three in the P/PB group (two events described
as stinging and one of a crawling sensation). Overall, both
products were well tolerated, which is supported by the
fact that only one participant declined a second application
(a 5-year-old treated with the EO/LP solution).
Trial 2: Efficacy after a single application
Following a single application of the EO/LP solution to the
hair of the 11 enrolled children, 1418 head lice were col-
lected. All lice were observed to be putatively dead as they
were wet-combed out of the hair. All head lice were re-
examined 30 min after combing was finished and were
confirmed dead, as shown in Table 5.
Skin irritancy and sensitisation study
Altogether 56 participants were enrolled and 53 completed
the study. There were three male and 53 female
participants aged 28 to 74 years. The three participants
who did not complete the study withdrew due to reasons
not related to the study protocol. No erythema, oedema or
adverse reactions of any kind were observed during the
course of the study. Therefore, when tested under semi-
occlusive conditions, the EO/LP solution can be considered
to be non-irritating and non-sensitising to the skin.
Paediatric testing
Nine boys and 11 girls aged from 6 months to 4 years were
enrolled in the study, with five children in each age group;
6–12 months; 12–24 months; 2–3 years and 3–4 years. All
children completed the study. No test-related irritation was
observed by the paediatrician and no safety-related com-
ments were made by any participants or their parents or
guardians at any time during the course of the study.
Therefore, the EO/LP solution can be considered to be safe
for the use on children’s hair and scalp.
In vitro ovicidal and pediculicidal efficacy
Table 6 shows that no body louse eggs hatched 10 days
following a 10-s immersion in the EO/LP solution. How-
ever, following immersion in water, 24, 76, 92 and 92%
body louse eggs hatched after 7, 8, 9 and 10 days, respec-
tively. The EO/LP solution was therefore found to be 100%
ovicidal compared with the water control when tested
under the conditions described.
The data in Table 7 show that 60 min following a 10-
min exposure to the EO/LP solution 100% of the body lice
were moribund or dead, while all the body lice treated
Table 5 Trial 2: Number of head lice detected by wet-combing
following a single application of the EO/LP solution
Subject
Number of head lice detected by wet-combing
Alive
†
Moribund
‡
Dead
§
10 0 10
20 0 17
3 0 0 320
4 0 0 663
50 0 5
60 0 7
70 0 16
80 0 8
9 0 0 360
10 0 0 12
11 0 0 0
Total 0 0 1418
†
Alive, able to move and right itself when rolled onto its back;
‡
moribund, cannot right itself when rolled onto its back;
§
dead, no
movement of any kind. EO/LP, eucalyptus oil and Leptospermum
petersonii.
Table 4 Trial 1: Cure rates for the primary and secondary effi-
cacy end-points for intention-to-treat participants
Treatment
Primary
end-point
†
n/n,%
Secondary
end-point
‡
n/n,%
EO/LP solution 35/49 (71) 27/49 (55)
P/PB mousse 16/48 (33) 19/48 (40)
Pvalue 0.0002 0.1259
†
The cure rate 7 days after the last application, i.e. day 14 for
the P/PB mousse and day 21 for the EO/LP solution.
‡
The cure rate
at day 1 for both products as diagnosed by visual inspection and
dry-combing of the hair and scalp. EO/LP, eucalyptus oil and Lep-
tospermum petersonii; P/PB, pyrethrins and piperonyl butoxide.
Table 6 The percentage of hatched louse eggs up to 10 days fol-
lowing a 10-s immersion in either the EO/LP solution or water
(n=100 eggs each for EO/LP solution and water control)
Treatment
Percentage of hatched eggs
Day 6 Day 7 Day 8 Day 9 Day 10
EO/LP solution 0 0000
Water control 0 24 7
*
76 4
*
92 8
*
92 8
*
*P<0.0001. Results presented as mean SEM. EO/LP, eucalyp-
tus oil and Leptospermum petersonii.
Table 7 Mortality of body lice 60 min following a 10-min expo-
sure to either the EO/LP solution or water (n=100 lice for the
EO/LP solution, n=50 lice for water control)
Treatment
Alive
†
(%)
Moribund
‡
(%) Dead
§
(%)
Corrected
mortality
¶
(%)
EO/LP
solution
0 25.3 2.5
*
74.7 2.5
*
100
*
Water
control
100 0 0 0
*P<0.0001. Results presented as mean SEM.
†
Alive, able to
move and right itself when rolled onto its back;
‡
moribund, cannot
right itself when rolled onto its back;
§
dead, no movement of any
kind;
¶
corrected mortality (%), ([% alive in water control –% alive
in test]/% alive in water control) 9100. EO/LP, eucalyptus oil and
Leptospermum petersonii.
Australian essential oils for head lice 5
©2017 Ego Pharmaceuticals Pty Ltd. Australasian Journal of Dermatology published by John Wiley & Sons, Ltd. on behalf of The
Australasian College of Dermatologists.
with water were alive. Although a moribund louse is not
yet dead, preliminary studies of up to 24 h showed that if a
louse is moribund after 20 min, it is significantly incapaci-
tated and death is imminent. The EO/LP solution was
therefore found to be 100% pediculicidal compared with
the water control (P<0.0001) when tested under the con-
ditions described.
DISCUSSION
Recent reviews have indicated the substantial lack of evi-
dence on the efficacy and safety of alternative head lice
treatments, with most of the few randomised controlled tri-
als found to be of low validity.
24,25
Furthermore, a review
by the Therapeutic Goods Administration of Australia
found that clinical trials conducted on the effectiveness of
head lice treatments were complicated by inconsistencies
and methodological flaws, including inappropriate defini-
tions of infestation, failure to exclude inappropriate
patients, failure to standardise treatments and the failure
to choose an appropriate end-point for efficacy measure-
ments;
17
conclusions that are also recognised by the wider
scientific community.
26,27
Trial 1 was designed to address these concerns and
included strict criteria for study entry, standardised treat-
ment and assessment regimes, sibling treatment, where
appropriate, and the use of a primary efficacy end-point
defined as the complete absence of live head lice 1 week
after the final treatment.
In Trial 1 the EO/LP solution was shown to be more
than twice as effective in curing head lice infestations as
the P/PB mousse, as measured by the complete absence of
head lice assessed by wet-combing 1 week after the final
treatment. In vitro tests confirmed the potent ovicidal and
pediculicidal activity of the EO/LP solution.
Overall, the two treatments were well tolerated by partic-
ipants with few adverse events reported. Adverse events
were generally mild and transient, and limited to itching,
stinging or burning and no serious or systemic adverse
events were reported. Repeat insult patch tests using the
EO/LP solution reported no irritation or sensitisation in
adults and paediatric testing also reported no irritation, fur-
ther highlighting the safety profile of the EO/LP solution.
Pyrethrins are neurotoxins derived from chrysanthemum
flowers.
28
They are formulated with piperonyl butoxide to
provide a synergistic effect. Pyrethrins modify voltage-
gated sodium channels by keeping the channel open for
abnormally long periods, leading to the spastic paralysis
and death of head lice.
28
Pyrethrins were quite effective
when introduced in the 1940s; however, the relatively low
effectiveness which was observed in Trial 1 reflects the
development of resistance in head lice, which has been
documented in Australia
6,29
and worldwide.
7–11
Resistance
has grown rapidly, with susceptibility patterns varying sub-
stantially between countries and even between schools.
28
The low results for the P/PB mousse could also be, in part,
due to the rigorous design features of the clinical study,
including the hard end-point definition for cure as mea-
sured 1 week after the last treatment application.
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.
17
The mechanism of action of essential oils is
unknown; however, the essential oils used in the EO/LP
solution are volatile and do not remain on the scalp after
treatment. This property, along with the fact that the EO/
LP solution is lethal to all head lice within a 10-min treat-
ment is unlikely to cause the rapid rise in resistance that
has been seen for traditional neurotoxic products.
So what is the cause of the 18% of treatment failures for
the EO/LP solution in Trial 1? The most likely reasons
could be (i) that some head lice survived any one of the
three treatments; (ii) that some eggs survived any one of
the three treatments and (iii) re-infestation. Trial 2 was
designed to examine specifically whether some head lice
survived any one particular treatment by wet-combing
after a single application of EO/LP solution. Wet-combing
hair with hair conditioner is considered the best technique
for diagnosing the presence of head lice.
18,19
Wet-combing
with hair conditioner is also used by some researchers to
obtain a supply of freshly caught head lice for further
research. It has been reported that most, if not all lice,
removed in this way can recover after capture.
30
All participants included in Trial 2 had live lice. The
number of head lice were not quantified prior to treat-
ment. However, following the application of the EO/LP
solution and washout no head lice were recovered using
wet-combing from one participant, and up to 663 head lice
recovered from another participant, that is, the initial
infestation ranged from light (<10 lice) to heavy (>600
lice). All 1418 head lice recovered from the 11 participants
were putatively dead on wet-combing from the hair and
did not recover when the conditioner was blotted from
them and they were allowed ample time to revive. This
indicates that the EO/LP solution kills 100% of head lice
irrespective of the degree of infestation in a single 10-min
treatment. Consequently, the 18% treatment failures asso-
ciated with Trial 1 may be attributed to the EO/LP solution
being incompletely ovicidal on the hairy scalp or re-infes-
tation of the participant prior to the final assessment.
Given that the in vitro studies indicate that the EO/LP
solution is 100% ovicidal after only a 10-s immersion, it is
more likely that the treatment failures are due to re-infes-
tation.
In conclusion, 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. The
small failure rate is possibly due to louse eggs surviving a
treatment on the hairy scalp, but it is most likely due to re-
infestation. The fact that the EO/LP solution is both vola-
tile and quickly effective means it is unlikely to cause the
development of head lice resistance in the community.
ACKNOWLEDGEMENT
The authors would like to thank Professor Stephen Barker,
Uniquest and Dr Phillip Altman, Altman Biomedical Con-
sulting, for their assistance in performing these studies.
6 KA Greive and TM Barnes
©2017 Ego Pharmaceuticals Pty Ltd. Australasian Journal of Dermatology published by John Wiley & Sons, Ltd. on behalf of The
Australasian College of Dermatologists.
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Australian essential oils for head lice 7
©2017 Ego Pharmaceuticals Pty Ltd. Australasian Journal of Dermatology published by John Wiley & Sons, Ltd. on behalf of The
Australasian College of Dermatologists.
