Effective treatment of head louse with pediculicides.

Of the pediculicides on the market, most are not 100% ovicidal and don't have a residual activity of more than 2 days. Therefore, at least 2 treatments are necessary to control the entire louse population. In order for a pediculicide to be effective it should kill all active stages of the louse after a single treatment. Otherwise remaining lice will continue laying eggs and the following treatments will not be fully effective, at least against the eggs. However, there is no general consensus as to when the second treatment should be conducted. Taking into consideration that head louse eggs hatch between 5 to 11 days, it is suggested that a second treatment should be administered 10 days after the beginning of the treatment. This might also explain why most of the clinical trials that were conducted by treating the patients twice with an interval of 6, 7, or 8 days showed a poor efficacy, and clinical trials where the pediculicide was applied with an interval of 10 days showed an efficacy level of more than 90%.