Pediculosis is an ectoparasitic infestation caused by three species of human lice: Pediculus humanus capitis (head louse), Pediculus humanus humanus/corporis (body louse), and Pthirus pubis (pubic/crab louse). Pruritus is the cardinal symptom, and diagnosis requires visualization of live lice — nits alone are insufficient to confirm active infestation. [1-2] Head lice are benign and not a health hazard; body lice are the only type that serve as a disease vector for potentially life-threatening infections. [3-4]
The following figure demonstrates the clinical presentations of body lice and other ectoparasitic infestations for comparison:
1. History
- Onset and duration of pruritus; location (scalp, body, pubic region)
- Timing: head lice pruritus may take 4–6 weeks to develop after initial infestation due to sensitization delay
- Triggers: head-to-head contact (head lice), sexual contact (pubic lice), poor hygiene/crowded conditions (body lice) [1][4]
- Prior treatments: OTC products used, technique, number of applications, retreatment interval
- Contacts: household members, classmates, sexual partners with similar symptoms
- Associated symptoms: scalp excoriations, secondary skin infections, sleep disturbance from nocturnal itching
- Important negatives: fever, rash elsewhere, joint pain (may suggest louse-borne systemic disease in body lice) [5]
2. Alarm Features
- Fever + body lice → consider louse-borne diseases: epidemic typhus (R. prowazekii), trench fever (B. quintana), relapsing fever (B. recurrentis) [4-5]
- Signs of secondary bacterial infection: cellulitis, impetigo, abscess formation, lymphangitis [5-6]
- Severe anemia in heavy body lice infestations (mean hemoglobin 2.5 g/dL lower than matched controls) [5]
- Epistaxis and thrombocytopenia in louse-borne relapsing fever [7]
- Pubic lice in a child → must evaluate for sexual abuse [8]
- Plica polonica (severely matted hair mass) in neglected head lice — may indicate neglect [6]
3. Medications
First-line (OTC)
- Permethrin 1% cream rinse — apply to affected area, wash off after 10 minutes; repeat in 9–10 days [3][9]
- Pyrethrins with piperonyl butoxide — same application; age ≥24 months [3]
Second-line (Prescription, for treatment failure or resistance):
- Topical ivermectin 0.5% lotion (Sklice) — single application, age ≥6 months; now available OTC [3][10]
- Spinosad 0.9% suspension (Natroba) — age ≥6 months; repeat at 7 days if live lice persist [3]
- Malathion 0.5% lotion (Ovide) — age ≥6 years; apply 8–12 hours; flammable [3][9]
- Oral ivermectin 200 μg/kg — repeat in 7–10 days; for children ≥15 kg; use with caution <15 kg [3]
Contraindicated/Avoid
- Lindane — not recommended due to neurotoxicity, especially in children <10 years, pregnant/breastfeeding women, and patients with extensive dermatitis [9]
- Animal-grade ivermectin products — never appropriate for human use [3]
- Products without FDA approval (home remedies, essential oils) lack evidence of efficacy [3]
Special populations
- Pregnancy: permethrin is first-line; oral ivermectin likely safe but limited data [3]
- Body lice: hygiene measures are primary treatment; pharmacotherapy alone is insufficient [5]
- Pubic lice: permethrin 1% or pyrethrins first-line; alternatives include malathion 0.5% or oral ivermectin 250 μg/kg [9]
4. Diet
- No specific dietary triggers or recommendations for pediculosis
- Ensure adequate iron and nutritional intake in patients with heavy body lice infestations and associated anemia [5]
5. Review of Systems
- Skin: pruritus location and severity, excoriations, rash, secondary infection signs
- Constitutional: fever, chills, malaise (body lice → systemic infection)
- HEENT: posterior cervical lymphadenopathy (head lice), conjunctivitis, eyelash involvement (pubic lice — phthiriasis palpebrarum) [11]
- MSK: leg pain, myalgias (trench fever) [12]
- GU: STI symptoms if pubic lice identified [1]
- Psych: sleep disturbance, social stigma, anxiety [3]
6. Collateral History and Family History
- Household contacts: examine and treat all symptomatic contacts; treat bed-sharing contacts empirically [3]
- School/daycare exposure: notify teachers/providers; "no-nit" policies are not recommended [1][3]
- Sexual contacts (pubic lice): evaluate and treat; screen for concurrent STIs [1][9]
- Social context: housing status, access to hygiene facilities, congregate living (shelters, prisons, refugee camps) — critical for body lice [5][12]
- No significant hereditary predisposition
7. Risk Factors
Head lice
- School-aged children (ages 3–11), especially girls [3]
- Head-to-head contact (sleepovers, sports, selfies)
- Not related to hygiene or socioeconomic status [3]
Body lice
- Homelessness, displacement, incarceration [5][12]
- Inability to change/wash clothing regularly
- Crowded living conditions, war, refugee settings [4]
- Mental illness, cognitive impairment, physical disability limiting ADLs [5]
Pubic lice
- Sexual contact (primary route) [1][8]
- Incidence declining with modern pubic hair grooming trends [8]
8. Differential Diagnosis
- Dandruff/seborrheic dermatitis — flakes are loosely adherent, not cemented to hair shaft like nits [3]
- Hair casts (pseudonits) — cylindrical, slide freely along hair shaft [3][6]
- Piedra (fungal infection of hair shaft) — firm nodules on hair [3]
- Scabies — burrows in web spaces, wrists, genitalia; worse at night; different distribution [1]
- Bedbug bites — linear papules on exposed skin; no lice/nits found [5]
- Contact dermatitis — distribution follows exposure pattern
- Atopic dermatitis — chronic, flexural distribution
- Delusional parasitosis — no organisms found on examination
- Artifacts: hairspray droplets, scabs, dirt, aphids caught in hair are commonly misidentified as nits [3]
9. Past Medical History
- Prior lice infestations and treatments used (resistance patterns)
- History of treatment failure with specific pediculicides
- Atopic dermatitis or eczema (may complicate treatment and mimic symptoms)
- Immunocompromised status (may affect severity)
- Seizure history (relevant if considering lindane, which is contraindicated)
- Liver disease (caution with oral ivermectin) [9]
10. Physical Exam
Head lice
- Use a fine-toothed louse comb (teeth 0.2–0.3 mm apart) — more sensitive and faster than visual inspection [3][13]
- Wet combing technique: comb/brush to remove tangles → insert comb at crown touching scalp → draw firmly down → examine comb after each stroke → systematically comb entire head at least twice [13]
- Look for live lice (1–3 mm, grayish-white, move quickly, avoid light) and nits (firmly cemented to hair shaft) [3]
- High-yield areas: behind ears, nape of neck [3]
- Nits >1 cm from scalp are unlikely to be viable [3]
- Posterior cervical lymphadenopathy, excoriations, secondary impetiginization
Body lice
- Skin lesions: excoriated papules, macules, hyperpigmentation, lichenification at lateral trunk waistline, legs, upper back/posterior shoulders with sparing of central/midback [5]
- Examine clothing seams (collar, arm openings, waist, pant legs) — this is where lice and nits are found; skin may have ≤10 lice [5]
Pubic lice
- Lice/nits on pubic hair; may also involve eyelashes, eyebrows, axillary hair, chest hair [8]
- Rust/brown deposits (feeding or fecal matter) [8]
- Maculae ceruleae (blue-gray macules) at bite sites — pathognomonic but uncommon [11]
11. Lab Studies
- Routine labs are not needed for uncomplicated head or pubic lice
- Body lice — consider:
- CBC (anemia — hemoglobin may be significantly lower) [5]
- Blood smear (if febrile — look for Borrelia spirochetes) [7]
- Blood cultures, Bartonella serology/PCR (if fever, endocarditis suspected) [5]
- LFTs (hepatic involvement in louse-borne infections) [7]
- Platelet count (thrombocytopenia in relapsing fever) [7]
- Pubic lice: STI screening — gonorrhea, chlamydia, syphilis, HIV, hepatitis B [1][9]
12. Imaging
- Not indicated for uncomplicated pediculosis
- Echocardiography if Bartonella endocarditis suspected in body lice patients with bacteremia [5]
- Dermoscopy (videodermatoscopy) can aid in distinguishing viable from nonviable nits and confirming diagnosis in uncertain cases [6]
13. Special Tests
- Wet combing with fine-toothed louse comb — gold standard diagnostic technique; more sensitive than visual inspection [3][13]
- Microscopy of submitted specimens — confirms species identification; many submitted "nits" are artifacts [3][14]
- Dermoscopy — can differentiate nits from pseudonits and assess nit viability [6]
- KOH preparation — if piedra (fungal hair infection) is in the differential [6]
14. ECG
- Not routinely indicated for pediculosis
- Consider ECG in body lice patients with fever and suspected louse-borne disease:
- Bartonella quintana endocarditis — may show conduction abnormalities [5]
- Epidemic typhus — myocarditis with tachycardia, arrhythmias [15]
- Louse-borne relapsing fever — myocarditis causing acute pulmonary edema [15]
15. Assessment
Clinical summary by type
Complications to consider
- Secondary bacterial infection (impetigo, cellulitis, abscess) [5-6]
- Iron deficiency anemia (heavy body lice) [5]
- Louse-borne infections: trench fever, relapsing fever, epidemic typhus [4-5]
- Psychosocial impact: stigma, school absenteeism, anxiety [3]
16. Treatment Plan
Head Lice — Stepwise Approach (per AAP 2022): [3]
- First-line: Permethrin 1% or pyrethrins + piperonyl butoxide OTC; repeat in 9–10 days
- Treatment failure: Switch class → topical ivermectin 0.5%, spinosad 0.9%, or malathion 0.5%
- Resistant to all topicals: Oral ivermectin 200 μg/kg, repeat in 7–10 days (weight ≥15 kg)
- Non-pharmacologic option: Wet combing with louse comb weekly × 3 weeks minimum [3]
- Environmental: Wash clothing/linens in hot water (≥130°F), dry on high heat × 20 min; seal non-washable items in plastic bag × 2 weeks; no extensive environmental decontamination needed [1][16]
Body Lice: [5]
- Primary treatment: Bathing + laundering clothing/bedding in hot water (≥130°F) weekly
- Provide clean clothing; seal infested items in plastic bag × 2 weeks
- Midpotency topical corticosteroids for itch
- Oral ivermectin or topical permethrin as adjuncts if hygiene measures alone are insufficient
- Treat secondary infections and screen for louse-borne diseases
Pubic Lice: [9]
- Permethrin 1% cream rinse or pyrethrins + piperonyl butoxide; wash off after 10 minutes
- Alternatives: malathion 0.5% (wash off after 8–12 hours) or oral ivermectin 250 μg/kg (repeat in 7–14 days)
- Treat sexual partners; screen for STIs
- Eyelash involvement: petrolatum ointment BID × 10 days or manual removal
17. Disposition
- Head lice and pubic lice: Discharge home with treatment and education in virtually all cases [3]
- No school exclusion for head lice — children may finish the school day and begin treatment at home; "no-nit" policies are not recommended [1][3]
- Admission criteria (rare, primarily body lice):
- Suspected louse-borne systemic infection (typhus, relapsing fever, trench fever) with hemodynamic instability, high fever, or end-organ dysfunction [7][15]
- Severe secondary bacterial infection (extensive cellulitis, abscess requiring I&D)
- Severe anemia requiring transfusion [5]
- Specialist consultation triggers:
- Dermatology: refractory cases after multiple treatment failures
- Infectious disease: suspected louse-borne systemic infection
- Ophthalmology: phthiriasis palpebrarum (eyelash involvement)
- Social work/child protective services: pubic lice in a child (evaluate for abuse) [8]
18. Follow Up / Return Precautions
- Follow-up timing: Re-examine in 1–2 weeks after treatment; monitor for 3 weeks total (one full louse life cycle = 21 days) [3]
- Treatment failure defined as: live lice detected within 3 weeks of completing appropriately administered therapy [3]
- Return precautions — seek care if:
- Live lice persist 8–12 days after completing treatment [16]
- Fever, redness, swelling, pain, or purulent drainage (secondary infection) [16]
- Worsening pruritus despite treatment
- Systemic symptoms (fever, malaise, headache) in body lice patients
- Patient counseling:
- Head lice are not a sign of poor hygiene and do not transmit disease [3]
- Nits may persist after successful treatment — this does not indicate failure [1][3]
- Check and treat all household contacts; treat bed-sharing contacts [3]
- Extensive home fumigation/environmental decontamination is unnecessary [1]
- Expected recovery: pruritus may persist for days after successful eradication due to residual hypersensitivity
References
1. Lice and Scabies: Treatment Update. — Gunning K, Kiraly B, Pippitt K. American Family Physician. 2019.
2. Pediculosis and Scabies: Treatment Update. — Gunning K, Pippitt K, Kiraly B, Sayler M. American Family Physician. 2012.
3. Head Lice. — Nolt D, Moore S, Yan AC, Melnick L. Pediatrics. 2022.
4. Ectoparasites: Pediculosis and Tungiasis. — Coates SJ, Thomas C, Chosidow O, Engelman D, Chang AY. Journal of the American Academy of Dermatology. 2020.
5. Scabies, Bedbug, and Body Lice Infestations: A Review. — Thomas C, Castillo Valladares H, Berger TG, Chang AY. The Journal of the American Medical Association. 2024.
6. Pediculosis Capitis: A Hidden Threat in Tropical Regions. — Logamoorthy R, Karthikeyan K. Clinical and Experimental Dermatology. 2026.
7. Epistaxis and Thrombocytopenia as Major Presentations of Louse Borne Relapsing Fever: Hospital-Based Study. — Abera EG, Tukeni KN, Didu GH, et al. PloS One. 2022.
8. A Clinical Review and History of Pubic Lice. — Patel PU, Tan A, Levell NJ. Clinical and Experimental Dermatology. 2021.
9. Sexually Transmitted Infections Treatment Guidelines, 2021. — Workowski KA, Bachmann LH, Chan PA, et al. MMWR. Recommendations and Reports : Morbidity and Mortality Weekly Report. Recommendations and Reports. 2021.
10. Common Pediatric Infestations: Update on Diagnosis and Treatment of Scabies, Head Lice, and Bed Bugs. — Ogbuefi N, Kenner-Bell B. Current Opinion in Pediatrics. 2021.
11. Pediculosis. — Ko CJ, Elston DM. Journal of the American Academy of Dermatology. 2004.
12. Infections in the Homeless. — Raoult D, Foucault C, Brouqui P. The Lancet. Infectious Diseases. 2001.
13. Head Lice. — Roberts RJ. The New England Journal of Medicine. 2002.
14. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). — Miller JM, Binnicker MJ, Campbell S, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2024.
15. Louse-Borne Relapsing Fever (Borrelia Recurrentis Infection). — Warrell DA. Epidemiology and Infection. 2019.
16. Head Lice. — Miller AE. JAMA Dermatology. 2025.