Abstract
Introduction
Head louse infection is diagnosed by finding live lice, as eggs take 7 days to hatch (but a few may take longer, up to 13 days) and may appear viable for weeks after death of the egg. Infestation may be more likely in school children, with risks increased in children with more siblings or of lower socioeconomic group. Factors such as longer hair make diagnosis and treatment more difficult.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical question: What are the effects of physically acting treatments for head lice? We searched: Medline, Embase, The Cochrane Library, and other important databases up to March 2014 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found six studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review, we present information relating to the effectiveness and safety of the following interventions: 1,2-octanediol, dimeticone, herbal and essential oils, and isopropyl myristate.
Key Points
Head louse infestation is diagnosed by finding live lice. Most eggs take 7 days to hatch (but a few may take longer, up to 13 days), and may appear viable for weeks after death of the egg.
Infestation may be more likely in school children, with risks increased in children with more siblings or of lower socioeconomic group. Factors such as longer hair make diagnosis and treatment more difficult.
Anecdotal reports suggest that prevalence during the 1990s has increased in most communities in Europe, the Americas, and Australasia. However, considerable differences are found between countries in terms of the number of products available, dosage form, and active substances used in treatment products.
For this review, we have focused on the evidence for the efficacy of some of the physically acting topical treatments for head lice and compared these with each other and some of the insecticides. There is interest in this type of treatment as resistance to one or more insecticides that act on the insect nervous system is now common in most developed countries.
In the US, there are no registered physically acting treatments for head lice (nearly all products being based on insecticides of one form or another), whereas in some countries in Europe (e.g., the UK) almost all treatments sold are currently based on physically acting principles.
In other European countries, there are varying mixes of physically acting and insecticide-based products available. In Australia, the majority of products are based on plant extracts and essential oils.
Generally the evidence for physically acting topical head lice treatments is weak. All of the RCTs we found were small and were sponsored by industry.
Interpretation of the results presents challenges due, for instance, to the variations in the formulations of products containing the same active treatment (e.g., lotions v mousses v shampoos; other included constituents, such as alcohols and conditioning agents; differing application procedures), reducing the quality of the evidence. Furthermore, there is some question about what exactly constitutes 'physically acting', as different authors describe the actions of some materials in different ways.
Dimeticone is a silicone and is a physically acting topical treatment working by occlusion. It does not act on the insect nervous system and is unlikely to be affected by resistance to older insecticides.
Dimeticone seems to be more effective at eradicating head lice compared with malathion or permethrin.
1,2-octanediol is a detergent that dissolves some components of the lipid waterproofing layer of the louse cuticle, reducing the ability of the louse to prevent water loss through the cuticle, and resulting in dehydration.
We found no direct information from RCTs meeting Clinical Evidence inclusion criteria on the effectiveness of any commercially available formulation of 1,2-octanediol in people with head lice infestation.
In general, we don’t know whether herbal and essential oils (we evaluated evidence on eucalyptus oil, tea tree oil, and tocopheryl acetate only) are effective at eradicating head lice compared with other treatments, as we found few RCTs. Efficacy is likely to depend upon the compound(s) or extracts used and the mode of action is unclear.
Isopropyl myristate (a physically acting treatment that may work by occlusion or by dissolving cuticle wax) may be more effective at eradicating head lice than permethrin, pyrethrum, or malathion, although the evidence is weak from a small number of trials.
Clinical context
General background
Head lice are obligate ectoparasites of socially active humans that infest the scalp and attach their eggs to the hair shafts. Conclusive diagnosis is made by finding live lice. Infestation occurs most frequently in school children and is largely harmless, although sensitisation reactions to louse saliva and faeces may result in localised irritation and erythema and secondary infection of scratches may occur.
Focus of the review
There are many different treatment options for head lice. Resistance to one or more insecticides, which have been traditionally used to manage head louse infestation, is now common in most developed countries. Therefore, for this review, we have focused on the evidence for some physically acting topical treatments, for which chemical resistance is not a concern. These treatments kill head lice by a physical rather than a chemical means, such as by occlusion of the louse respiratory system and prevention of excretion of water taken up when lice feed on blood. We have compared these physically acting treatments with each other and with some of the insecticides.
Comments on evidence
Generally, the evidence we found was weak. All of the RCTs we found were small and were sponsored by industry. There are variations in the formulations of products containing the same active treatment (e.g., lotions v mousses v shampoos; other included constituents, such as alcohols and conditioning agents; differing application procedures), which reduces the quality of the evidence. Furthermore, there is some question about what exactly constitutes 'physically acting', as different authors describe the actions of some materials in different ways.
Search and appraisal summary
The literature search was carried out in March 2014. For more information on the electronic databases searched and criteria applied during assessment of studies for potential relevance to the review, please see the Methods section. Searching of electronic databases retrieved 71 studies. After deduplication, 28 records were screened for inclusion in the review. Appraisal of titles and abstracts led to the exclusion of 18 studies and the further review of 10 full publications. Of the 10 full articles evaluated, no systematic reviews and six RCTs were included.
Additional information
The availability of different treatments varies widely between countries. Guideline recommendations in different countries also differ. In the UK, there is a difference in which treatments for head lice are available on prescription compared with over the counter.
About this condition
Definition
Head lice are obligate ectoparasites of socially active humans. They infest the scalp and attach their eggs to the hair shafts. Itching, resulting from multiple bites, is not diagnostic, but may increase the index of suspicion. Most eggs take 7 days to hatch (but a few may take longer, up to 13 days) and may appear viable for weeks after death of the egg. Therefore eggs glued to hairs, whether hatched (nits) or unhatched, are not proof of active infection. A conclusive diagnosis is made by finding live lice. One observational study compared two groups of children with lice eggs but no lice at initial assessment. Over 14 days, more children with five or more eggs within 6 mm of the scalp developed infestations compared with those with fewer than five eggs. Adequate follow-up examinations using detection combing are more likely to be productive than nit removal to detect and identify the need for treatment of any re-infestation. Infestations are not self-limiting. Various treatment options have been used that can broadly be divided into five groups as follows: topically applied insecticides; topically applied, physically acting agents; topically applied, homeopathic, plant formulations and other remedies; oral drugs; mechanical agents (combs, electronic devices, heating devices). This review focuses on the topically applied, physically acting agents.
Incidence/ Prevalence
We found no studies on incidence and few recently published studies of prevalence in resource-rich countries. Anecdotal reports suggest that prevalence has increased during the early 1990s in most communities in Europe, the Americas, and Australasia. A cross-sectional study from Belgium (6169 children aged 2.5–12.0 years) found a prevalence of 8.9%. An earlier pilot study (677 children aged 3–11 years) showed that, in individual schools, the prevalence was as high as 19.5%. One cross-sectional study from Belgium found that head lice were significantly more common in children from families with lower socioeconomic status (OR 1.25, 95% CI 1.04 to 1.47), in children with more siblings (OR 1.2, 95% CI 1.1 to 1.3), and in children with longer hair (OR 1.20, 95% CI 1.02 to 1.43), although hair length may primarily influence the ability to detect infestation. The socioeconomic status of the family was also a significant influence on the ability to treat infestations successfully — the lower the socioeconomic status, the greater the risk of treatment failure (OR 1.70, 95% CI 1.05 to 2.70).
Aetiology/ Risk factors
Observational studies indicate that infestations occur most frequently in school children, although there is no evidence of a link with school attendance. We found no evidence that lice prefer clean hair to dirty hair.
Prognosis
The infestation is largely harmless. Sensitisation reactions to louse saliva and faeces may result in localised irritation and erythema. Secondary infection of scratches may occur. Lice have been identified as primary mechanical vectors of scalp pyoderma caused by streptococci and staphylococci usually found on the skin.
Aims of intervention
To eliminate infestation by killing or removing all head lice and their eggs.
Outcomes
Eradication rate treatment success is given as the percentage of people completely cleared of head lice. This may be reported as proportion of people lice/louse-free at any point in time, or with no live lice present after last treatment. There are no standard criteria for judging treatment success or what constitutes infestation. Trials used different methods, and in some cases the full methodology was not reported. Few studies were pragmatic. Adverse effects.
Methods
Clinical Evidence search and appraisal March 2014. The following databases were used to identify studies for this systematic review: Medline 1966 to March 2014, Embase 1980 to March 2014, and The Cochrane Database of Systematic Reviews 2014, issue 2 (1966 to date of issue). Additional searches were carried out in the Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA) database. We also searched for retractions of studies included in the review. Titles and abstracts identified by the initial search, run by an information specialist, were first assessed against predefined criteria by an evidence scanner. Full texts for potentially relevant studies were then assessed against predefined criteria by an evidence analyst. Studies selected for inclusion were discussed with an expert contributor. All data relevant to the review were then extracted by an evidence analyst. Study design criteria for inclusion in this review were: published RCTs and systematic reviews of RCTs in the English language, at least single-blinded, and containing 20 or more individuals (10 in each arm), of whom more than 80% were followed up. There was no minimum length of follow-up. We excluded all studies described as 'open', 'open label', or not blinded unless blinding was impossible. We included RCTs and systematic reviews of RCTs where harms of an included intervention were assessed, applying the same study design criteria for inclusion as we did for benefits. In addition, we use a regular surveillance protocol to capture harms alerts from organisations such as the FDA and the MHRA, which are added to the reviews as required. To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. Readers should be aware of this when relating percentages to summary statistics such as relative risks (RRs) and odds ratios (ORs). We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table). The categorisation of the quality of the evidence (high, moderate, low, or very low) reflects the quality of evidence available for our chosen outcomes in our defined populations of interest. These categorisations are not necessarily a reflection of the overall methodological quality of any individual study, because the Clinical Evidence population and outcome of choice may represent only a small subset of the total outcomes reported, and population included, in any individual trial. For further details of how we perform the GRADE evaluation and the scoring system we use, please see our website (www.clinicalevidence.com).
Table.
GRADE Evaluation of interventions for Head lice.
Important outcomes | Eradication rate | ||||||||
Studies (Participants) | Outcome | Comparison | Type of evidence | Quality | Consistency | Directness | Effect size | GRADE | Comment |
What are the effects of physically acting treatments for head lice? | |||||||||
1 (73) | Eradication rate | Dimeticone versus malathion | 4 | –1 | 0 | 0 | 0 | Moderate | Quality point deducted for sparse data |
2 (235) | Eradication rate | Dimeticone versus permethrin | 4 | –1 | 0 | 0 | 0 | Moderate | Quality point deducted for early termination of one of the RCTs at 9 days |
1 (216) | Eradication rate | Herbal and essential oils versus malathion | 4 | –1 | 0 | –1 | 0 | Low | Quality point deduced for weak methods (all of the authors were employees of the pharmaceutical company that funded the trial); directness point deducted for unclear generalisability of the single specific essential oil |
1 (45) | Eradication rate | Herbal and essential oils versus permethrin | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data; directness point deducted for unclear generalisability of the single specific essential oil |
1 (123) | Eradication rate | Herbal and essential oils versus pyrethrum | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data; directness point deducted for unclear generalisability of the single specific essential oil |
1 (216) | Eradication rate | Isopropyl myristate versus malathion | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for weak methods (published author information includes the name of a pharmaceutical company that is also the name next to the isopropyl myristate-containing intervention used in the trial); directness point deducted due to intervention containing various other chemicals |
1 (168) | Eradication rate | Isopropyl myristate versus permethrin | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data; directness point deducted for early termination of 1 RCT |
1 (60) | Eradication rate | Isopropyl myristate versus pyrethrum | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
We initially allocate 4 points to evidence from RCTs, and 2 points to evidence from observational studies. To attain the final GRADE score for a given comparison, points are deducted or added from this initial score based on preset criteria relating to the categories of quality, directness, consistency, and effect size. Quality: based on issues affecting methodological rigour (e.g., incomplete reporting of results, quasi-randomisation, sparse data [<200 people in the analysis]). Consistency: based on similarity of results across studies. Directness: based on generalisability of population or outcomes. Effect size: based on magnitude of effect as measured by statistics such as relative risk, odds ratio, or hazard ratio.
Glossary
- Low-quality evidence
Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
- Moderate-quality evidence
Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
- Pragmatic RCT
An RCT designed to provide results that are directly applicable to normal practice (compared with explanatory trials that are intended to clarify efficacy under ideal conditions). Pragmatic RCTs recruit a population that is representative of those who are normally treated, allow normal compliance with instructions (by avoiding incentives and by using oral instructions with advice to follow manufacturers' instructions), and analyse results by 'intention to treat' rather than by 'on treatment' methods.
- Scalp pyoderma
Scalp pyoderma involves impetigo-like bacterial infections that result from scratching. In most cases they are caused by streptococci, with some staphylococcal involvement. Scalp pyoderma of this type is closely associated with long-term louse infestation.
Disclaimer
The information contained in this publication is intended for medical professionals. Categories presented in Clinical Evidence indicate a judgement about the strength of the evidence available to our contributors prior to publication and the relevant importance of benefit and harms. We rely on our contributors to confirm the accuracy of the information presented and to adhere to describe accepted practices. Readers should be aware that professionals in the field may have different opinions. Because of this and regular advances in medical research we strongly recommend that readers' independently verify specified treatments and drugs including manufacturers' guidance. Also, the categories do not indicate whether a particular treatment is generally appropriate or whether it is suitable for a particular individual. Ultimately it is the readers' responsibility to make their own professional judgements, so to appropriately advise and treat their patients. To the fullest extent permitted by law, BMJ Publishing Group Limited and its editors are not responsible for any losses, injury or damage caused to any person or property (including under contract, by negligence, products liability or otherwise) whether they be direct or indirect, special, incidental or consequential, resulting from the application of the information in this publication.
Contributor Information
Ian F. Burgess, Insect Research & Development Limited, Cambridge, UK.
Paul Silverston, Anglia Ruskin University, Cambridge, UK.
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