Head lice control - least toxic options

Head lice problems are often incorrectly associated with lack of cleanliness. An understanding of non-toxic chemical alternatives, and ways of treating and reducing risk of re-infestation, can help children and parents manage head lice outbreaks.

Biology
Head lice (Pediculus capitis) are human ectoparasites and live exclusively on the human head, dining regularly on human blood. They are wingless insects, coloured tan to greyish-white, have six legs ending in claws and are up to 3mm in length. The female lays her eggs, attaching each egg to a separate hair using a glue-like substance. Female head lice lay approximately six eggs per day, producing an average of 56 eggs per insemination. The tear-shaped eggs hatch after seven to 10 days and take between six to 12 days to pass through the nymphal stages to become adults. Eleven to 18 hours after maturing the female is ready to mate and lays the first eggs a further 11 to 18 hours later(1).
    As they do not fly, head lice are transmitted by close head contact. The bites are not painful, but the saliva can cause allergic reactions that result in itching. Scratching can lead to skin damage and serve as an entry for germs, and in severe head lice cases individuals may feel tired and irritable. Children aged 4-16 are most likely to suffer from head lice, although they can easily spread to the rest of the family. Outbreaks may be greater in the autumn, when children return to school, before any strategies have been employed to control the problem(2).

Chemical controls
In 1994/95 the UK market for head lice chemicals was £14.4 million, rising to £29.7 million in the period 1997/98. In 1998/99 nearly 10 million doses were applied with just over six million on the National Health Service(3).
    Four pesticide active ingredients are licensed for use by the Department of Health's Medicines Control Agency against head lice: carbaryl, malathion, permethrin and phenothrin. These substances are designed to kill lice and their eggs, and may be harmful to humans especially when they are applied to the head where the scalp is particularly permeable. Children have less well developed immune systems, underdeveloped detoxification mechanisms and rapid growth, and are more susceptible and sensitive to the toxic effects of pesticides.
    In recent years the Pesticide Exposure Group of Sufferers (PEGS) has received many complaints of pesticide exposure that have been linked to head-lice treatments. Symptoms reported include burning sensations, skin irritation, headaches, dizziness, hyperactivity, increased susceptibility to infection and general malaise, with acute hallucinatory reactions linked to malathion and corneal damage following treatment with synthetic pyrethroids.
    Malathion, an organophosphate insecticide, is a cholinesterase inhibitor and has been found to disrupt the immune system(4). In 1991 the US Environmental Protection Agency classified permethrin as a potential human carcinogen. German studies link exposure to permethrin and phenothrin with leukaemia, lymphoid cancer and multiple chemical sensitivity(5). In November 1995, the UK government's Committee on Carcinogenicity concluded that carbaryl is a potential human carcinogen. As a result, the Department of Health announced that head lice products containing carbaryl were restricted to prescription only. This followed reports of an association between family use of carbaryl in the home, garden and pet care, and childhood cancer(6). The licence for carbaryl use in agriculture and the home environment is being withdrawn by the Pesticides Safety Directorate because the manufacturers will not supply up-to-date data to support continued approval.
    In the past the monitoring, diagnosis and treatment prescription for head lice in UK children was carried out by school nurses. These responsibilities have now been removed from school nurses without effective replacement, and children and their parents either resort to mainstream medical practitioners, or pharmacists, or their own judgement to deal with the problem. The results are often inadequate and may in the long term exacerbate it.

Treatments used in the UK
carbaryl (carbamate) laboratory evidence of carcinogenicity,
mutagenicity, teratogenicity, endocrine disruption, cholinesterase inhibitor
malathion (organophosphate) cholinesterase inhibitor,
very toxic orally, possible carcinogen, mutagen and endocrine disrupter
permethrin (synthetic pyrethroid) possible carcinogen,
skin sensitiser, endocrine disrupter, mild eye and skin irritant
phenothrin (synthetic pyrethroid) possible endocrine disruptor

There is strong evidence that licensed treatments claiming to kill lice and their eggs in a single application do not necessarily do so. Louse populations become resistant to regularly encountered pesticides by groups (for example, resistance to the cholinesterase inhibitor carbaryl confers resistance to the similarly acting malathion; permethrin resistance embraces phenothrin because they are both synthetic pyrethroids). Constant use of permethrin is particularly likely to promote resistance, since it relies on bonding with the hair to kill lice coming in contact with it as they emerge from eggs. Lice which encounter a faded residual effect survive the sub-lethal dose, promoting the development of resistance in subsequent generations. This situation leads to repeat treatments and use of one pesticide after another on the same individual, increasing pesticide exposure(7).
    It is particularly worrying that health professionals are urged to "Prescribe sufficient quantity for two applications" as the Prescribing Nurse Bulletin does and, for example, suggests two applications of malathion, followed by two applications of phenothrin or permethrin, followed by two applications of carbaryl when all else has failed, and as a last resort mechanical removal(8).

Natural head lice control
Safe and effective alternatives are available, which do not rely on the application of dangerous chemicals to the scalp. The non-profit organisation Community Hygiene Concern (CHC) has developed a programme based on systematic removal of hatched lice, to break the life cycle.
    CHC claims that seven year-olds can be successfully taught to detect hatched lice by wet combing(9). They call this 'bug busting' (see Bug Busting Kit box). A child then needs help to follow through and clear the lice. The principle of the system is based on three simple facts:

• thoroughly wet lice slow down and become easy to hook off with a fine toothcomb
• removing lice before they mature prevents them from mating and spreading
• co-ordinated action by a community using this method helps prevent re-infestation.

Ordinary shampooing and conditioning are used to wet the hair and any lice thoroughly (this procedure ensures that the lice, which tend to stay near the scalp, are bathed in moisture). Preparatory wide-tooth combing with conditioner untangles and straightens the hair. Then systematic fine tooth combing from the hair roots to the tips over the entire head removes hatched lice. Insects caught in the comb are wiped or rinsed off before the next stroke to avoid combing them back on again. The conditioner is rinsed off and the head combed again while the hair is still wet. The process is repeated on a four-day cycle over two weeks. At the end of this period all life stages of the lice should have been removed, and no unhatched eggs should remain in the hair.

Other natural products
Battery operated lice combs, which detect and stun lice, are non-toxic, and have recently come onto the market.
    Headlice products on the market that are made from natural substances such as essential oils cannot necessarily be presumed effective. Joanna Ibarra, Programme Co-ordinator of CHC, says: "Neither the conventional synthetic pesticide medicines nor the 'natural' alternatives that are currently in use are fully effective against head lice and their eggs; this is leading to application after application being poured onto vulnerable heads. Treatments should all be used with special caution on infants, during pregnancy and breast-feeding and people with asthma, eczema and allergies".

Comment
Safe and effective methods of head lice control, such as the Bug Busting Kit, should be supported under health systems (for example, available free on a GP prescription) and publicised widely in chemists shops. This would make the products widely accessible to families who wish to protect their children from the harmful effects of pesticides. Medicinal head lice products that contain pesticides should be withdrawn from use or, at the very least, restricted to prescription only.

References
1. J. Figueroa, S. Hall and J. Ibarra (Eds), Primary health care guide to common UK parasitic diseases, Community Hygiene Concern, December 1998, 75pp.
2. Ibid.
3. House of Commons Green Network Presentation, 1 July 1999.
4. C. Swadener, Low doses of malathion disrupt immune system function, Journal of Pesticide Reform, 12, 3, 1992.
5. Household spray cancer link, Pesticides News 28, June 1995.
6. J.R. David, R.C. Brownson, R. Garcia, B.J. Bentz and A. Turner, Family pesticide use and childhood brain cancer, Archives of Environmental Contamination and Toxicology, 1993, 24, 87-92.R.
7. Community Hygiene Concern, Information supporting early day motion 798, March 1995.
8. Management of head louse infection, Prescribing Nurse Bulletin, 1999, 1, 13-16.
9. J. Ibarra, Coping with head lice in the 1990's, Primary Health Care, 4:4, April 1994.

[This article first appeared in Pesticides News No.45, September 1999, p18-19]