Pediculus humanus capitis is the insect responsible for head lice. During the female louse's 30-day lifespan, she lays approximately 10 eggs per day and attaches each of them with a gluelike, waterproof substance to human hair, 1 mm from the scalp. Larvae emerge 8 to 10 days later from these nits, or eggs, which remain firmly attached to hair.
No topical agent has been shown to be 100% ovicidal.1 The existence of any nits, a major aspect of lice infestations, signifies the potential that this contagious malady may still be present. Many schools, therefore, adhere to a "no-nit" policy before children can reenter the classroom after infestation, thereby imposing prolonged absenteeism. Insecticides fail to kill all nits and larvae because they act on the insects' central nervous systems, which are not fully developed in the first 4 days of the insects' existence. Several products, namely, Clear lice egg remover gel (Care Technologies, Greenwich, Conn), Step 2 (Genderm, Lincolnshire, Ill), and a 50/50 mixture of vinegar and water, have been suggested as beneficial in nit removal. However, no clinical benefit has been documented in the medical literature.2
Burkhart CN, Burkhart CG, Pchalek I, Arbogast J. The Adherent Cylindrical Nit Structure and Its Chemical Denaturation In Vitro: An Assessment With Therapeutic Implications for Head Lice. Arch Pediatr Adolesc Med. 1998;152(7):711-712. doi:10.1001/archpedi.152.7.711