Dimethicone

When applied topically, dimethicone forms a layer to delay the evaporation of water. In the treatment of head lice dimethicone 100, the respiratory systems of head lice are targeted. NYDA works by suffocating the lice, nymphs and the embryos. The physical properties of this drug, including the viscosity and spreading property of the solution allow it to easily flow into the respiratory system of all developmental stages of the insect, causing suffocation and death of the organisms. It diffuses through the stigmata (spiracles) of the lice, into the tracheae of the head lice as well as through the aeropyles of the egg operculum. The solution then displaces oxygen. The low viscosity, volatile dimethicone enables the NYDA head lice solution to penetrate into the breathing system. Its evaporation causes the thickening of the NYDA solution. The remaining high viscosity dimethicone ultimately encloses the respiratory system and thus leading to suffocation of all stages of head lice (adult lice, larvae and eggs). This mode of action prevents the development of lice resistance by preventing the formation of new progency.

Studies performed using house crickets and lice suggest a close correlation between the death of the lice and the influx of the solution into the insect head tracheae. These data strongly suggest that the total filling of the head tracheae immediately blocks the oxygen supply to the insect central nervous system. Death, following numerous stages of disability after the entrance of dimethicones into the abdominal tracheal system, demonstrates the sequence of oxygen deprivation. NYDA was applied directly to the head and mouth of the organism, and was found to have no effect when applied solely to the outside of the head/mouth.