Hedrin once spray gel is a fast acting solution that gets to work in just 15 minutes this thicker gel formulation contains dimeticone and penetrol to penetrate head lice eggs and kills head lice with just one application the hedrin range is proven in clinical trials to be incredibly effective at killing head lice but is specially formulated to suit your preference and lifestyle each product contains a physical mode of action that lice cannot develop a resistance to they do not require combi