Scabies and lice are among the most undertreated conditions in medicine — not because the treatments are difficult, but because the exposure network is not addressed. Treating only the index patient while leaving household contacts untreated guarantees reinfestation within days.
CLINICAL PRINTABLE
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A one-page Scabies / Lice clinical reference is on the way.
1 · Recognition
- Scabies: intensely pruritic rash, worse at night. Burrows (thin, wavy, thread-like lines) in web spaces of fingers, wrists, periumbilical area, genitalia, and axillae. Spares the face in adults (involved in infants and immunocompromised).
- Scabies in immunocompromised patients (crusted/Norwegian scabies): hyperkeratotic, crusted plaques with thousands to millions of mites. Highly contagious. Standard permethrin dosing is inadequate — requires oral ivermectin plus topical therapy.
- Head lice (Pediculus humanus capitis): pruritus of the scalp, nape of neck, and behind the ears. Nits (eggs) cemented to hair shafts close to the scalp. Live lice are difficult to find. Primarily affects school-age children.
- Pubic lice (Pthirus pubis): pruritus in the pubic area. Nits and lice visible on pubic hair. Sexually transmitted. Screen for other STIs.
- Body lice (Pediculus humanus corporis): lice live in clothing seams, not on the body. Associated with poor hygiene and homelessness. Vector for Rickettsia prowazekii (epidemic typhus), Bartonella quintana (trench fever), and Borrelia recurrentis (relapsing fever).
2 · Differential / Mimics
Atopic dermatitis
Chronic, relapsing pruritic rash with flexural distribution. No burrows. Personal/family atopy history. Does not respond to scabicidal treatment.
Contact dermatitis
Pruritic rash at site of allergen or irritant exposure. Distribution follows exposure pattern. No burrows or nits.
Folliculitis
Pustules centered on hair follicles. No burrows. Culture may identify causative organism.
Dermatitis herpetiformis
Intensely pruritic vesicles on extensor surfaces. Associated with celiac disease. Responds to dapsone and gluten-free diet, not scabicidal treatment.
3 · Treatment Pathway
Scabies — Standard treatment
Permethrin 5% cream: apply from neck to toes (include face/scalp in infants), leave on 8–14 hours, then wash off. Repeat in 1 week. Treat ALL household members and close contacts simultaneously on the same day, regardless of symptoms.
Scabies — Alternative/adjunct
Oral ivermectin 200 mcg/kg: two doses 1–2 weeks apart. Preferred for crusted scabies (combine with permethrin), treatment failures, or when topical application is impractical. Not approved in children <15 kg or pregnant women.
Scabies — Environmental decontamination
Wash all clothing, bedding, and towels used in the past 3 days in hot water (>50°C) and dry on high heat. Items that cannot be washed: seal in plastic bag for 72 hours (mites cannot survive >3 days off a host). Vacuum upholstered furniture.
Scabies — Post-treatment pruritus
Pruritus may persist for 2–4 weeks after successful treatment due to ongoing immune reaction to dead mites and eggs. This is NOT treatment failure. Oral antihistamines and topical corticosteroids for symptom relief. Do not retreat within 1 week.
Head lice — Treatment
Permethrin 1% lotion or pyrethrin shampoo: apply to dry hair, leave 10 minutes, rinse. Repeat in 9–10 days to kill newly hatched nymphs. Nit combing with fine-toothed comb after treatment. Treat all household members with confirmed lice.
Head lice — Resistance/failure
Permethrin resistance is common. Alternatives: malathion 0.5% lotion, benzyl alcohol 5% lotion, spinosad 0.9% suspension, or oral ivermectin. Spinosad and benzyl alcohol do not require nit combing.
Pubic lice
Permethrin 1% cream rinse or pyrethrin shampoo. Apply to affected area, leave 10 minutes, rinse. Repeat in 9–10 days. Treat sexual partners. Screen for other STIs.
4 · Expected Response
- Scabies: new lesions should not appear after 48–72 hours of successful treatment. Pruritus persists 2–4 weeks — this is expected and does not indicate treatment failure.
- Head lice: no live lice should be found 24 hours after treatment. Nits may remain attached to hair shafts but should be non-viable. Nit combing removes dead eggs.
- Treatment failure: new burrows appearing after 2 weeks, or live lice found after 24 hours, indicates true failure. Consider resistance, inadequate application, or reinfestation from untreated contacts.
5 · Escalation
- Crusted (Norwegian) scabies: dermatology referral for combined oral ivermectin plus topical permethrin protocol. Infection control measures for healthcare settings — standard precautions are insufficient.
- Secondary bacterial infection (impetigo, cellulitis) complicating scabies or lice: treat with appropriate antibiotics (topical mupirocin for localized, oral antibiotics for extensive or systemic infection).
- Institutional outbreaks (nursing homes, schools, shelters): public health notification and coordinated simultaneous treatment of all residents and staff.
Apply It · Change One Detail
APPLY IT
A 7-year-old child is brought in with intense nighttime itching and a rash between the fingers and on the wrists. The mother also has itching. Scabies is the diagnosis. Treating only the child will result in reinfestation from the mother within days. The entire household — mother, father, siblings — must be treated simultaneously on the same day with permethrin 5%, regardless of whether they have symptoms yet.
CHANGE ONE DETAIL
Change one detail — the same child has itching only on the scalp, and the mother finds small white specks cemented to the hair shafts near the nape of the neck. This is head lice, not scabies. Permethrin 1% lotion applied to the hair, repeated in 9–10 days, plus nit combing. Household members with confirmed lice are treated; asymptomatic members do not require prophylactic treatment.
Bottom Line
Treating only the index patient guarantees reinfestation. All household members and close contacts must be treated simultaneously on the same day.
EVIDENCE & REFERENCES
- Gunning K, et al. Lice and scabies: treatment update. Am Fam Physician. 2012;86(6):535-541.
- CDC. Parasites — Scabies. Treatment. Centers for Disease Control and Prevention. 2020. https://www.cdc.gov/parasites/scabies/treatment.html