Over 98% of US head lice are now permethrin-resistant. This 2026 CDC-verified guide covers Sklice ivermectin 0.5% OTC lotion (94.9% louse-free at Day 15, single application, no nit combing required), oral ivermectin off-label dosing by weight, a 7-treatment comparison table, why permethrin no longer works, and complete household decontamination steps.