What head lice treatments are available?

Chemical insecticide: malathion

Resistance to neurotoxic chemical insecticides has increased to the point where malathion is the only one still in use for eradication of head lice. Permethrin crème rinse, although still marketed, is no longer recommended in the BNF for this indication.

Malathion is an organophosphorus compound – a potent cholinesterase inhibitor that prevents the breakdown of acetylcholine and interferes with neuromuscular transmission in the head louse, paralysing it and preventing it from feeding. It is oil- soluble and absorbed by passive diffusion through the lipid coat of both insect and egg. It is poorly absorbed through human skin, and much more efficiently detoxified by human metabolic processes than by those of insects. It is therefore safe for occasional or intermittent use at low concentrations as a pediculicide.

There are no contraindications to the use of malathion, apart from known sensitivity. Malathion is available as an aqueous lotion. It is applied to dry hair and allowed to dry naturally over at least 12 hours. It is then shampooed or rinsed out and dead lice and eggs are combed out. The treatment should be repeated after seven days.