Hedrin Once Spray Gel is a liquid gel in an easy spray format with penetrol to boost egg kills. The easy to use trigger helps to direct the liquid gel onto the head and hair even in those hard to get areas. The formula is highly effective against head lice and eggs. In some cases, head lice have become resistant to many existing treatments which may result in infestations within schools and communities taking longer to eradicate. However, because Hedrin works in a purely physical way, resistance is not a factor and efficacy not diminished. It deals with every phase of head lice: detection, treatment, post treatment & protection.