Pediculicides and scabicides: application, retreatment and laundry

Separate the lice technique from the scabies technique

For head lice, permethrin lotion is applied to damp hair and scalp after shampooing, left for a short time as directed and rinsed off. CDC advises rinsing over a sink with warm rather than hot water to limit skin exposure. A fine-toothed nit comb removes dead lice and eggs afterwards.

For scabies, a stronger permethrin cream is applied in a thin layer to the whole body from the neck down, including skin folds, between fingers and toes and under nails, then washed off after eight to fourteen hours. Infants and older adults may also need the scalp and face treated. Confusing these techniques is a common exam trap.

Before applying anything, confirm the diagnosis and check for broken skin, other skin conditions, age and pregnancy, because these affect which product is suitable. Use enough product to cover the area fully but no more than directed, and keep a record of the date so retreatment can be timed accurately.

Explain retreatment timing by the life cycle

Many lice products do not kill eggs, so lice that hatch after treatment can restart the infestation. CDC recommends retreatment when the product does not kill nits, usually seven to ten days after the first application, timed to catch newly hatched lice before they can lay eggs. Some prescription products, such as spinosad or ivermectin lotion, often need less retreatment.

For scabies, a second application about one week later may be prescribed, and oral ivermectin is an alternative given as two doses spaced as prescribed. Crusted scabies needs combined, more intensive treatment under close supervision. Teach families not to use extra product or combine several products unless instructed.

Prepare families for itch after scabies treatment

Itching after scabies treatment does not usually mean the treatment failed. CDC notes that itching commonly continues for two to four weeks because the skin reaction to dead mites and their products takes time to settle. Families who misunderstand this may reapply cream repeatedly, causing skin irritation without benefit.

Teach that new burrows or new lesions appearing after about two weeks, or worsening rather than gradually improving itch, should be reviewed. Watch for secondary bacterial infection from scratching, such as spreading redness, warmth or pus. Prescribers may recommend measures to ease itching; report breathing difficulty or signs of infection promptly.

Teach laundry, contacts and product safety

For scabies, all close contacts are treated at the same time, even without symptoms, because mites spread through prolonged skin contact. Clothing, towels and bedding used in the previous days are washed in hot water and dried on a hot setting, or sealed in a bag for at least 72 hours. For lice, wash recently used clothing and bedding in hot water and check other household members.

Keep products away from eyes, nose, mouth and mucous membranes, and do not use lice lotions on eyebrows or eyelashes. Some lice products have age limits, and malathion is flammable, so hair dryers and open flames are avoided during use. Check pregnancy status and age before recommending any product.

Work a hypothetical scabies follow-up question

Imagine a hypothetical eight-year-old treated for scabies with permethrin cream ten days ago, along with the whole family. The parent says the child still itches at night and asks whether to apply the cream again tonight. Options include reapplying immediately, explaining that itch can persist for weeks while checking for new burrows, or starting a different scabicide. Explaining and assessing is strongest.

Reapplying without evidence of active infestation risks skin irritation. Switching products assumes failure that has not been shown. The plan changes if new burrows appear or the itch is worsening after two weeks, which warrants prescriber review for possible retreatment or an alternative diagnosis.

Sources and further reading

MedlinePlus: Permethrin Topical. Different lice and scabies techniques, contact time, areas to avoid, laundry, nit combing, contacts and itch after treatment.

CDC: Clinical care of head lice. Over-the-counter and prescription options, age limits, malathion flammability, retreatment when nits are not killed and warm-water rinsing.

CDC: Clinical care of scabies. Neck-down permethrin application, repeat application, oral ivermectin, treating contacts together, itch lasting weeks and laundry or 72-hour bagging.