Full marks solution gets rid of head lice in just 5 minutes. Cyclomethicone (a silicone-based substance) and isopropyl myristate are the active ingredients and work by dissolving the outer coating of the head lice, which dehydrates and kills them. They can then be removed along with any eggs using the Full Marks removal comb supplied. Head lice cannot become resistant to Full marks because it works in this physical way, unlike conventional insecticides for head lice which poison the parasites by chemical means.