Head lice infestation occurs in all age groups, but especially in elementary school children. In most cases, transmission occurs by head-to-head contact.1
Pyrethrins are natural extracts from chrysanthemum flowers that are neurotoxic to lice. They are available over the counter (OTC), usually combined with piperonyl butoxide (Rid, and generics) to enhance their activity (Box). Pyrethrins are unstable in heat and light, do not kill all unhatched eggs, and require multiple treatments because they have no residual activity. Allergic reactions occur rarely in patients with ragweed or chrysanthemum allergy. Resistance to pyrethrins is now widespread.
Drugs for Head Lice. JAMA. 2017;317(19):2010–2011. doi:10.1001/jama.2016.18589