Licenders Lice Shampoo works on lice because of a special enzyme known as protease. Protease enzyme is produced naturally by arthropods as a means to open their exoskeleton. The Licenders’ lice removal products contains Citronella Oil, which is one of the essential oils obtained from the leaves and stems of different species of Cymbopogon. Citronella oil is a renowned plant-based insect repellent, and has been registered for this use in the United States since 1948.The United States Environmental Protection Agency considers oil of citronella as a biopesticide with a non-toxic mode of action. Research also indicates that citronella oil is an effective repellent for head louse.