What kills louse eggs? - briefly
Heat above 130 °F (54 °C) for at least five minutes, or washing with hot water followed by high‑heat drying, eradicates nits. Chemical agents such as permethrin or dimethicone also penetrate the egg shell and cause mortality.
What kills louse eggs? - in detail
Lice eggs, commonly called nits, adhere tightly to hair shafts and resist many superficial treatments. Effective eradication requires agents that either penetrate the protective shell, disrupt embryonic development, or physically destroy the egg structure.
Chemical agents that have proven activity against nits include:
- Permethrin 1 % lotion – neurotoxic insecticide; applied to scalp for 10 minutes, then rinsed. Residual activity reduces hatching but may be less effective against resistant strains.
- Pyrethrins with piperonyl‑butoxide – synergistic formulation; requires a 10‑minute exposure. Works by blocking sodium channels in embryonic nerve cells.
- Malathion 0.5 % – organophosphate; leaves a film that interferes with acetylcholinesterase. Recommended for a 10‑minute soak, followed by thorough rinsing.
- Spinosad 0.9 % – derived from bacterial fermentation; binds to nicotinic acetylcholine receptors, causing paralysis. Applied for 10 minutes, then washed off.
- Ivermectin 0.5 % – macrocyclic lactone; inhibits glutamate‑gated chloride channels. Requires a 10‑minute contact period; useful when resistance to pyrethroids is documented.
- Benzyl alcohol 5 % – suffocates developing embryos; left on scalp for 10 minutes before rinsing. Does not rely on neurotoxic mechanisms, reducing resistance concerns.
- Dimethicone 4 % – silicone‑based polymer; coats the egg, blocking respiration and causing desiccation. Applied for 10 minutes, then removed with a fine‑tooth comb.
Physical methods that guarantee destruction of eggs:
- Steam treatment – exposure to saturated steam at 100 °C for at least 5 minutes penetrates the shell and denatures proteins. Commercial steam devices calibrated to maintain temperature prevent scalp burns.
- Hot‑air drying – hair dryer set to maximum heat (≈ 70 °C) directed at the scalp for 10 minutes reduces hatchability. Effectiveness depends on consistent temperature across the entire head.
- High‑temperature laundering – washing clothing, bedding, and hats in water ≥ 60 °C, followed by dryer heat ≥ 70 °C for 30 minutes, eliminates residual eggs in the environment.
Mechanical removal remains essential:
- Nit combs – metal or fine‑tooth plastic combs with teeth spaced 0.2–0.3 mm. Repeated passage through damp hair, followed by rinsing of comb after each stroke, physically extracts eggs. Comb must be used after chemical or heat treatment to remove compromised nits.
Environmental control measures:
- Seal non‑washable items in plastic bags for two weeks, depriving eggs of viable conditions.
- Vacuum carpets, upholstery, and car seats to remove stray hairs containing nits.
- Replace or launder personal items (hats, scarves, pillowcases) in hot water and dry on high heat.
Combining a neurotoxic or suffocating chemical with a heat‑based approach, followed by meticulous combing, yields the highest eradication rate. Monitoring for re‑infestation over a 14‑day period ensures that any surviving eggs are detected and treated promptly.