Hedrin Xpress is a colorless liquid that is highly effective against head lice and their eggs. It works by physically suffocating the lice. Additionally, it contains Penetrol, which helps the product penetrate the lice eggs and kill them. Hedrin is effective with just one application; however, a follow-up should be conducted after a week to ensure that no lice or eggs have escaped the treatment process. If live lice are found, the treatment should be repeated. The gel can be used as often as necessary without the lice developing resistance.