Head lice or pediculus humanus capitis, occurs in as many as 12 million children yearly nationwide. Lice are spread by direct contact with hair that is infested. Activities such as sharing combs, brushes, beds and hats may also contribute to the spread of these parasites. Lice infestations in the U.S. are more frequent in girls and leads to social disruption by stigmatizing infested children and causing parental anxiety, loss of income because of the need to care for the child at home and absenteeism from school or day care.1,2
The life cycle of a louse is divided into three stages. The female adult louse lays eggs (nits) that hatch after eight or nine days. The young louse (nymph) matures into adulthood within nine to twelve days. The adult louse usually lives about one month and feeds on human blood. Adult lice are usually tan to grey in color and two to three millimeters in length. Nits are usually yellow to white in color and are less than one millimeter in size. Lice typically die without access to a human blood after one to two days. Lice do not appear to cause disease but subsequent bacterial infections may occur from scratching.
Signs and symptoms of a head lice include tickling on the scalp, difficulty sleeping and excessive scratching. Diagnosis can be difficult as a louse moves quickly and blends in with the hair shaft. Nits typically are found one-fourth inch from the scalp during active infestations. All family members should be evaluated for lice if one child has an infestation.
Newly approved Sklice Lotion 0.5 percent (ivermectin) may be used in children who are six months and older. A recent study has suggested that a single topical application of ivermectin kills most of the lice.3 In this study, two parallel trials were done in patients with head lice, to investigate the efficacy and safety of a single application of a new 0.5% ivermectin lotion formulation as compared with vehicle control, which is an identical formulation without ivermectin. Eligible patients were healthy persons 6 months of age or older with head louse infestation who agreed not to use any other louse treatment, comb out nits, cut or chemically treat hair during the study. The researchers found that 94.9% of ivermectin treated patients were louse free 1 day after application and there was significant reduction in itching between day 1 and day 2 in the ivermectin group, as compared with the vehicle-control group, which may be due to the removal of the lice. The proportion of head louse free patients in the ivermectin group was 85.2% on day 8 and 73.8% on day 15. The continued efficacy of treatment with topical ivermectin 2 weeks after a single treatment suggests that this formulation has activity against louse eggs. Another recent laboratory study has suggested that ivermectin has activity against louse eggs. In this study ivermectin was applied to head louse ova, although the ova subsequently hatched, all the released nymphs quickly died. The nymphal mortality was attributed to ivermectin induced mouthpart paralysis, which severely limited or completely prevented feeding of nymphs.4
In conclusion, topical ivermectin showed high efficacy within 24 hours, with most treated patients remaining louse free through the final assessment, 2 weeks after a single treatment, without the need for nit combing.
Older over the counter treatments (permethrin based) are also available but typically require two applications because they are not ovacidal. Nits must be removed to prevent re-infestation. Two over the counter products for use in children are Pyrethrins/Piperonly butoxide for children two years of age or older and Permethrin lotion 1% for children two months old or older. But, more often, lice are showing significant resistance to permethrin and pyrethrins.
Other recommendations include washing bedding, clothes, hats etc in hot water. Hot air cycles should be used for the dryer. Items that cannot be laundered may be dry cleaned or placed in plastic sealed bags for two weeks to allow time for all lice life cycles to be completed. Vacuuming floors and furniture to remove infested hair is also recommended.
Sonia Shoukat M.D.
Thomas W. Hale Ph.D.
1) Frankowski BL, Weiner LB. Head lice. Pediatrics 2002;110:638-643.
2) Gordon SC. Shared vulnerability: a theory of caring for children with persistent head lice. J Sch Nurs 2007;23:283-292.
3) David M. Pariser, M.D., Terri Lynn Meinking, Ph.D., Margie Bell, M.S., and William G. Ryan, B.V.Sc. Topical 0.5% Ivermectin Lotion for Treatment of Head Lice. N Engl J Med 2012; 367:1687: 10.1056/NEJMoa1200107.
4) Strycharz JP, Berge NM, Alves A, Clark JM. Ivermectin acts as a posteclosion nymphicide by reducing blood feeding of human head lice (Anoplura: Pediculidae) that hatched from treated eggs. J Med Entomol 2011;48: 1174-1182.