Permethrin is supposed to leave a residue ... Unlike Rid, Nix does not contain piperonyl butoxide. If OTC products don’t treat your lice or if infestations come back repeatedly, consider asking ...

Active ingredients to look for include pyrethrin, piperonyl butoxide, fipronil, indoxacarb, boric acid, abamectin, hydramethylnon, clothianidin, or imidacloprid. Here's where to find those ...