You can use Lyclear whenever it is required for head lice infestations, as indicated within the direction for use. Normally, 1 or 2 treatments (depending on the treatment chosen) will suffice to get rid of head lice.
However, it is possible that people who have been treated can get head lice again from other untreated people they come into close contact with. In this case, you can use Lyclear again and it will still be as effective.