Chemical Insecticides

These poison lice by chemical means. In the UK the only currently recommended chemical insecticide is Malathion 0.5% aqueous liquid. There is evidence that head lice are becoming resistant to chemical insecticides so their use may not be as effective as in previous years.

As with the physical insecticides these should be applied to all of the scalp and all of the hair (root to tip). The product should be left on for the manufacturer’s recommended time and then washed off. Multiple applications at least 7 days apart may be recommended.

Advantages:

• Suitable for people of all ages and people with asthma or skin conditions. The manufacturer states that there are no known effects in pregnancy and lactation so if dimeticone and wet combing are infective this could be used for pregnant and breast feeding patients.

• No evidence of serious systemic adverse reactions are associated with use

Disadvantages:

• Low cure rates due to resistance have been reported

• Has an unpleasant smell