How does lice and nit shampoo work? - briefly
The shampoo introduces an insecticidal agent—often a neurotoxin such as permethrin or a silicone‑based coating like dimethicone—that penetrates the exoskeleton, disrupts nerve function, and quickly immobilizes adult lice. At the same time, surfactants lower surface tension, breaking the adhesive that secures nits to hair shafts and enabling their removal.
How does lice and nit shampoo work? - in detail
Lice and nit shampoos contain chemicals that target the nervous system of head‑lice and disrupt the protective coating of eggs. The most common neurotoxic agents are pyrethrins, permethrin, or carbaryl; they bind to voltage‑gated sodium channels on the insect’s nerve membranes, causing prolonged depolarization and paralysis. Dimethicone, a silicone‑based compound, works by coating the lice and nits, filling the respiratory spiracles and preventing gas exchange, leading to death without neurotoxicity.
The ovicidal effect results from two mechanisms. First, neurotoxic ingredients penetrate the porous shell of the egg, reaching the developing embryo and causing paralysis before hatching. Second, silicone‑based agents physically block the operculum, the small opening through which the nymph emerges, preventing emergence even if the embryo survives.
Application steps ensure optimal efficacy:
- Wet the hair thoroughly; excess water dilutes the active concentration.
- Apply the shampoo uniformly, ensuring contact with the scalp and all hair shafts.
- Massage gently for the time specified on the label (typically 5–10 minutes) to allow absorption.
- Rinse completely; do not use regular conditioner or other hair products immediately after rinsing.
- Comb the hair with a fine‑toothed nit comb while still damp to remove dead lice and detached eggs.
- Repeat the treatment after 7–10 days to eliminate any newly hatched lice that survived the first application.
Resistance to pyrethroid compounds has been documented in some populations; formulations that combine neurotoxic agents with dimethicone provide a broader spectrum of action and reduce the likelihood of treatment failure. Safety considerations include avoiding contact with eyes and mucous membranes, limiting use in children under the age recommended by the product, and following label instructions regarding frequency of re‑application.
In summary, lice‑and‑nit shampoos act by chemically incapacitating adult insects, penetrating egg shells to kill developing embryos, and physically suffocating both stages through silicone coating. Proper application and a scheduled repeat dose are essential to achieve complete eradication.