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As a direct result of the lice developing resistance, many of the synthetic products used to treat head lice are now ineffective. This is because resistant lice are able to survive a much higher dose of the active ingredient.
Synthetic, insecticidal head lice treatments can be split into three different types:
- Organophosphates such as treatments containing Malathion.
- Synthetic pyrethroids such as treatments containing Phenothrin and Permethrin.
- Carbamates such as treatments containing carbaryl.
In the past if head lice failed to respond to one treatment, it was possible to switch to another. However, multiple-resistance is now common whereby lice can be resistant to a combination or all of these treatments.
All recent studies of head lice products in the UK have concluded that none of the current chemical based treatments are fully effective. The most widely used treatments, the pyrethroids and organophosphates, are particularly poor, with success rates of 13% and 36% respectively (Downs et al, 1999). |
