Yes, preparations containing permethrin (the active ingredient) are highly effective at killing live head lice. However, while permethrin is very successful against active lice, it is less effective at killing the unhatched eggs (nits). To ensure complete clearance, a second application is typically recommended 7 to 9 days after the first treatment to kill any newly hatched lice before they can reproduce. Additionally, using a fine-toothed nit comb to physically remove the eggs is highly recommended. Please follow the instructions carefully, and rest assured that head lice are very common, harmless, and easily treatable.