Why don't lice go away? - briefly
Lice persist due to rapid reproduction, resistance to common insecticides, and the attachment of their eggs (nits) to hair shafts, which hinders complete removal.
Why don't lice go away? - in detail
Lice remain present because their life cycle aligns with human hair growth, allowing rapid population expansion. An adult female lays 6‑10 eggs (nits) per day; each egg hatches in 7‑10 days, producing a nymph that reaches maturity within another 7‑10 days. This 2‑week generation time enables a small infestation to become noticeable within weeks.
Egg adhesion contributes to persistence. Nits are cemented to the hair shaft with a proteinaceous glue that resists removal by washing or combing. The glue hardens within hours, making mechanical removal difficult without specialized fine‑toothed combs and systematic effort.
Resistance to insecticides limits chemical control. Repeated exposure to common pediculicides (e.g., permethrin, pyrethrins) has selected for mutations in the lice’s voltage‑gated sodium channels, reducing susceptibility. Alternative treatments (spinosad, ivermectin, silicone‑based lotions) are required when resistance is confirmed.
Re‑infestation from close contact maintains the problem. Lice transfer through head‑to‑head contact, shared hats, combs, or bedding. Even after successful eradication of an individual’s infestation, contact with untreated carriers quickly restores the population.
Environmental conditions support survival. Lice thrive at temperatures between 28 °C and 32 °C, typical of the scalp. They cannot survive off the host for more than 24‑48 hours, but this window is sufficient for transmission via personal items.
Effective management combines several actions:
- Mechanical removal: Daily use of a nit‑comb for 10‑14 days, each session lasting several minutes, dislodges nits and live insects.
- Chemical treatment: Application of a proven pediculicide according to label instructions, repeated after 7‑10 days to eliminate newly hatched nits.
- Resistance testing: Consultation with a healthcare professional when standard treatments fail, to identify resistant strains and select alternative agents.
- Environmental decontamination: Washing bedding, hats, and personal items in hot water (≥ 60 °C) or sealing them in plastic bags for 48 hours to kill any surviving lice.
- Education and monitoring: Informing all close contacts about detection signs and encouraging simultaneous treatment to prevent cross‑contamination.
Persistence results from the combination of rapid reproductive capacity, sturdy egg attachment, chemical resistance, and ease of transmission among individuals sharing close contact. Comprehensive, repeated interventions targeting each factor are essential to achieve lasting elimination.