Scabies and Lice: How to Identify and Eradicate These Parasitic Infestations

It’s not just about itching. When you or someone you live with starts scratching nonstop-especially at night-it’s rarely just dry skin. More often than not, it’s scabies or lice. These aren’t rare, old-fashioned problems. In 2023, the World Health Organization estimated 204 million people worldwide had scabies. In the U.S. alone, 6 to 12 million children get head lice every year. And here’s the thing: if you treat one person and ignore everyone else, you’re just setting up a cycle of reinfection.

What Exactly Are Scabies and Lice?

Scabies isn’t caused by dirt. It’s caused by a tiny mite called Sarcoptes scabiei var. hominis. These mites burrow into your skin, lay eggs, and trigger an allergic reaction that makes you itch like crazy-especially at night. The classic sign? Wavy, grayish lines on your skin, often between fingers, on wrists, around the waist, or on genitals. In babies, the rash can cover the whole body. In elderly or immunocompromised people, it can turn into crusted scabies, where millions of mites pile up and the skin becomes thick, scaly, and contagious beyond normal.

Lice are different. There are three kinds:

• Head lice (Pediculus humanus capitis)-most common in kids 3 to 11. They cling to hair, not skin, and spread through direct head-to-head contact.
• Body lice (Pediculus humanus corporis)-rare in developed countries. They live in clothes and bedding, not hair. You get them from poor hygiene or crowded living conditions.
• Pubic lice (Phthirus pubis)-also called crabs. They live in coarse body hair: pubic area, armpits, beard. Mostly spread through sexual contact.

Both scabies and lice are contagious. But they don’t jump. They crawl. You get them from close contact: sharing beds, clothes, towels, or sitting on a couch someone with lice just left.

How Are They Treated?

The good news? Both are treatable. The bad news? Many treatments don’t kill the eggs. That means you need to do more than one treatment.

Scabies Treatment: Permethrin vs. Ivermectin

The go-to treatment for scabies is permethrin 5% cream. You apply it from the neck down, covering every inch of skin-including under nails, between fingers, and the genital area. Leave it on for 8 to 14 hours, then wash it off. Repeat after 7 days. Why? Because the eggs hatch in about 3 to 4 days, and the new mites need to be killed before they lay more eggs.

Studies show permethrin cures about 92.5% of cases after two applications. But it’s messy. People skip spots. Some forget to reapply. A 2022 audit from a California dermatology clinic found 12.3% of treatment failures were due to improper application.

Enter oral ivermectin. It’s not FDA-approved for scabies, but doctors use it all the time. You take it by mouth-200 micrograms per kilogram of body weight-on an empty stomach, then again 7 to 14 days later. It’s especially useful for people who can’t apply cream (like those with dementia or severe eczema) or in outbreaks (nursing homes, shelters). One study of 242 patients in Iran showed a 85.9% cure rate after one dose, jumping to 100% after the second.

There’s also topical ivermectin 1%-a lotion you apply like permethrin. A 2023 study found it works just as well: 92.5% cure rate. It’s less messy, easier for kids, and doesn’t require full-body coverage.

For crusted scabies, you need both. Doctors combine oral ivermectin with permethrin cream. Dosing varies by severity, but often it’s two to three doses of ivermectin spaced two weeks apart.

Lice Treatment: Permethrin, Spinosad, and the Rise of Resistance

Head lice have become harder to kill. In many U.S. areas, 15 to 30% of lice are resistant to permethrin. That’s why alternatives matter.

• Spinosad 0.9% liquid (approved in 2019) kills both lice and eggs in one application. No need to comb. Just apply to dry hair, leave for 10 minutes, rinse. Safe for kids as young as 4.
• Oral ivermectin is now used off-label for lice too. A 2020 study in the Solomon Islands found a double dose (0.4 mg/kg) wiped out 95-100% of head lice.
• Dimethicone and natural oils (like coconut or tea tree) are popular in home remedies, but there’s little solid proof they work consistently.

For body lice, washing clothes and bedding in hot water (at least 130°F) and drying on high heat kills lice and eggs. No medicine needed-just hygiene.

Why Treatment Fails (And How to Avoid It)

Most treatment failures aren’t because the medicine doesn’t work. They’re because of human error.

• Not treating everyone. If Mom gets treated but the kids don’t, the mites or lice come right back. Everyone who had close contact-family, roommates, partners-must be treated at the same time.
• Washing off too soon. Permethrin needs 8-14 hours to work. Showering after 2 hours? You’re wasting your time.
• Missing spots. Scabies mites hide in finger webs, under nails, under breast folds, around the waistline. You have to cover every crease.
• Not cleaning the environment. Scabies mites can live off the body for up to 72 hours. Wash bedding, towels, and clothes worn in the last 3 days in hot water. Dry on high heat. Items you can’t wash? Seal them in plastic bags for 7 days.

One study of nursing home outbreaks found that when staff treated everyone at once and cleaned everything, eradication rates hit 98.7%. When they treated only the symptomatic, it dropped to 42%.

What About Side Effects?

Permethrin is generally safe. Some people report mild burning or tingling. About 18% of users in a 2022 survey said it felt uncomfortable.

Ivermectin can cause nausea, dizziness, or diarrhea. In one review, 8.3% of users reported stomach upset. It’s not recommended for children under 15 kg or pregnant women because safety data is limited.

Lindane lotion? It’s banned in many places-including the U.S.-because it can cause seizures. Don’t use it unless every other option has failed.

What’s New in Treatment?

The field is evolving. Researchers are testing new drugs that kill eggs-something current treatments can’t do. Three compounds are in Phase II trials as of late 2023.

Mass treatment programs are showing promise. In the Solomon Islands, giving azithromycin (for trachoma) and ivermectin (for scabies) together cut scabies rates by over 95%. That’s a model other countries are watching.

And the global market? It’s growing. The scabies treatment market was worth $287 million in 2022 and is expected to grow over 5% yearly. Permethrin still leads, but ivermectin and spinosad are gaining ground fast.

When to See a Doctor

You can try over-the-counter lice treatments at home. But if:

• You’ve tried two treatments and the lice are still there,
• Your child has scabies and is under 2 years old,
• You or someone has thick, crusted skin (possible crusted scabies),
• You’re pregnant or breastfeeding,

then see a doctor. Prescription treatments work faster and safer.

Prevention Tips

• Avoid sharing hats, combs, towels, or bedding.
• Check kids’ heads weekly during school outbreaks.
• Don’t panic if you find one louse. Treat immediately, don’t wait for a full infestation.
• For scabies, if someone in your home has it, treat everyone-even if they don’t itch yet. Symptoms can take 4-6 weeks to appear in first-time cases.

These aren’t diseases of poor hygiene. They’re diseases of close contact. And they’re treatable-if you do it right.