Physical insecticides: dimeticone

Dimeticone is a long-chain linear silicone and is used as a physical pediculicide. There are two types of formulation:

• 4% dimeticone in a volatile silicone base (cyclomethicone). It appears to act by coating the insects and thus disrupting their ability to breathe and to absorb and excrete water. It does not kill eggs, so a second application is recommended seven days after the first.
• 92% dimeticone penetrates the respiratory system of adult lice and nymphs, and into the pores of eggs, causing suffocation. It is left on the hair overnight. A second application may not be necessary.

Other constituents of physical pediculicides include:

• Octane-1,2 diol, an alkyl diol surface-active agent that appears to act by disrupting cuticular lipid on both head lice and their eggs, resulting in dehydration.
• Cyclomethicone/isopropyl myristate. Cyclomethicone is a cyclic polydimethylsiloxane. Isopropyl myristate is an ester of myristic acid, an essential fatty acid derived from palm kernel oil and isopropyl alcohol. These compounds disrupt the lipid coating that covers the head louse exoskeleton and protects it against water loss, resulting in dehydration.
• Oxyphthirine is a formulation containing dimeticone, caprylic triglyceride (a component of coconut oil), and diisopropyl adipate. As with other silicone-based products, it attaches to the respiratory orifices of lice and eggs to suffocate and dehydrate them.