Ectoparasite treatment fails for social reasons far more often than pharmacological ones. A child treated for head lice returns to the same classroom and the same bed; a patient treated for scabies goes home to untreated family members. Both come back and are recorded as treatment failure.
The rule is the same for both: treat the household on the same day, whether or not they itch, and repeat the treatment at the interval the drug requires — a week for permethrin and for ivermectin, because neither reliably kills eggs. For head lice, wet combing with conditioner every three days for two weeks does more than any single application and is free, which matters where the drug is not.
The other half is the conversation. Both conditions carry stigma, and a family told only what to apply will not tell the school, the neighbours or the other household. Say explicitly that infestation is not a matter of hygiene, that everyone sharing a bed or a room needs treating, and that itching for two weeks afterwards is expected. Without that, the prescription is the easy part and the reinfestation is inevitable.
- Treat all household and close contacts on the same day, symptomatic or not
- Repeat at seven days: neither permethrin nor ivermectin reliably kills eggs
- Add wet combing every three days for two weeks in head lice
- Say plainly that infestation is not about hygiene, or families will not tell contacts
- Warn that itch persists for one to two weeks after cure, so it is not read as failure
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