Lice, Pediculosis, Pediculus humanus capitis, Pediculus humanus corpus, Phthirus pubis Infestation, Head Lice, Phthirus pubis, Body Louse Infestation, Pediculus Capitis Infestation, Body Lice, Genital Lice, Pubic Lice, Pubic Louse, Crab Louse, Pediculosis Pubis, Pediculosis Ciliaris, Eyelash Phthiriasis, Phthiriasis palpebrarum

  • See Also
  • Epidemiology
  1. Head Lice will infect up to 10-40% of school children in the United States
  2. Greatest Incidence is in the Fall in U.S.
  • Background
  1. Lice is not typically a sign of uncleanliness (exception is Body Lice in cramped living conditions)
  2. Lice does not typically transmit disease (rare exception is Body Lice and Typhus)
  3. Main effect of lice is one of embarrassment
  4. Lice do not jump or fly and are not passed by pets
  • Risk Factors
  1. Demographics
    1. Ages affected: 3 to 11 years
    2. Girls more affected than boys
    3. African Americans are uncommonly affected
  2. Hair type and color
    1. Brown or red hair color (more than black or blond)
    2. Fine hair
    3. Clean hair on healthy children
    4. Hair length is unrelated to lice infestation risk
  • Pathophysiology
  • Lice Life Cycle
  1. Images
    1. louse.jpg
  2. Louse Lifetime: 1 month
  3. Lice feed on blood
    1. Typical feeding every 3-6 hours
    2. Survival 15-20 hours without a blood meal
    3. Survival beyond 48 hours without blood meal is rare
  4. Adult female may lay 150 eggs within 1 month (3-10/day) at the skin-hair junction
    1. Female applies strong glue for nit attachment to hair
  5. Nits incubate
    1. Temperature >82 degrees Fahrenheit
    2. Humidity >70%
    3. Viable Embryo
      1. Shows movement within nit
      2. Eye spots may be seen on Embryo
  6. Nits hatch after 7-14 days of incubation
    1. Attach to Hair Shaft adjacent to scalp
    2. Hair Growth moves nit away from scalp
    3. Nit >0.25 inches from scalp is old nit
      1. Not active infestation
    4. Empty nit left when Embryo departs
      1. Distal nit appears flat (missing operculum)
      2. No movement from within nit and no eye spots seen
  7. Nymphs mature into adults in 3 stages over 12 days
  8. Lice life cycle repeats every 3 weeks
  • Pathophysiology
  • Transmission - Mechanism of transfer
  1. Lice cannot jump or fly
  2. Close contact person to person transmission
    1. Requires direct head contact
  3. Shared inanimate objects (nits survive <2 days)
    1. Combs
    2. Hats
    3. Brushes
    4. Towels
  • Types
  1. Head and Body Lice are interchangeable
    1. Head Lice (Pediculus humanus capitis)
      1. Female lays eggs at base of hair
      2. Egg adheres as hair grows
      3. Transmitted by fomites or head to head contact
    2. Body Lice (Pediculus humanus corpus)
      1. Live in seams of clothing or bedding which they briefly leave only to feed on human host
      2. Transmitted by contact (most common in crowded living conditions with poor hygiene)
      3. May carry Typhus (Rickettsia)
  2. Genital Lice: Crab Louse (Phthirus pubis)
    1. Typically seen in younger adults
    2. Often transmitted as Sexually Transmitted Disease
    3. May also affect eyelashes (Pediculosis Ciliaris, Eyelash Phthiriasis, Phthiriasis palpebrarum)
  • Symptoms
  1. General
    1. Pruritus is due to delayed Hypersensitivity Reaction to louse Saliva
    2. Pruritus starts at least 2 weeks after infestation with first episode
      1. May be delayed up to 6 weeks with initial exposure
      2. Subsequent infestations are associated with Pruritus within the first 1-2 days after exposure
    3. May be accompanied by a nonspecific dermatitis (Erythematous Macules, Papules, wheals)
    4. Scratching due to Pruritus may result in secondary infections
  2. Head Lice
    1. Pruritus at occiput, scalp, and post-auricular
  3. Body Lice
    1. Pruritus may lead to secondary infection
  4. Genital Lice
    1. Mild to severe regional Pruritus
  5. Eyelash Lice (Pediculosis Ciliaris, Eyelash Phthiriasis, Phthiriasis palpebrarum)
    1. May be confused with Seborrheaor blepharoconjunctivitis
  • Signs
  1. Pearls for examination
    1. Use bright light and a magnifying glass for best visualization
    2. Consider combing the hair with a fine-toothed, nit comb to identify lice
    3. Yellow-white empty egg casings may be easiest to see
    4. Diagnosis of lice infestation relies on finding live lice
      1. Nits (lice eggs) alone are not sufficient for diagnosis
      2. Nits may remain on hair for months despite successful treatment
  2. Head Lice
    1. Nits visualized with greater ease than lice
      1. White dots or grains fixed to the Hair Shaft near their base
      2. Fluorescent under Wood Lamp
    2. Adult lice are 3-4 mm in size (sesame seed size)
    3. Locations (within 1 cm of scalp)
      1. Around and behind ears
      2. Nape of neck
    4. Associated findings
      1. Lymphadenopathy (esp. suboccipital)
  3. Body Lice
    1. Signs of secondary infection may occur
    2. Same size as Head Lice
  4. Genital Lice
    1. Much shorter than head and Body Lice
    2. Distribution
      1. Genital region and lower Abdomen
      2. Occasionally axillae or eyelashes (Pediculosis Ciliaris, Phthiriasis palpebrarum)
    3. Characteristics
      1. Maculae ceruleae (gray-blue Macules) may occur
  • Complications
  1. Iron Deficiency Anemia
  2. Typhus, a Rickettsial infection (from Body Lice)
  • Management
  • General
  1. See Nit Removal below
  2. Confirmation of diagnosis requires visualizing at least one live louse
    1. Nits and egg casings alone are not sufficient for active lice diagnosis
    2. Only a small percentage (<20%) of those with nits alone (no live lice) will develop active infestations
      1. Williams (2001) Pediatrics 107(5): 1011-5
  3. Environmental care (prudent but not proven) of items in contact with head within 2 days of treatment
    1. Machine wash all washables (e.g. hats, linen, clothing) in hot water (130 F or 54 C)
      1. Dry on hot cycle in dryer
    2. Store exposed un-washables in plastic bags for 2 weeks
    3. Vacuum all affected areas including furniture (no special carpet treatments needed)
    4. Soak combs and brushes in hot water (130 F or 54 C) for 15 min
    5. Not necessary to fumigate or to spray furniture with pediculocides
  4. Screening exposures
    1. Examine family members and close school contacts and treat if lice identified
    2. Children should not miss school for lice infestation (per AAP)
    3. Treat sexual partners of those with Genital Lice (Pediculosis Pubis)
  • Management
  • Medications
  1. See Nit Removal Below
  2. First-line Medications
    1. Precautions
      1. Resistance to topical Permethrin and Pyrethrin is very high in the U.S. as of 2014-2016
      2. Some argue these agents should no longer be used for lice
      3. However OTC preparations are still effective in many cases and are low risk and inexpensive
      4. Feldmeier (2014) Am J Clin Dermatol 15(5):401-12 +PMID: 25223568 [PubMed]
    2. Permethrin 1% (Nix) - OTC (effective in 90% of cases)
      1. Mechanism: Neurotoxic to lice
      2. Shampoo hair (no conditioner) and towel dry
      3. Apply Permethrin cream rinse and rinse in 10 min
      4. Safe down to age 2 months old
      5. Requires second treatment in 9-10 days (kills newly hatched lice)
    3. Pyrethrins 0.3% with Piperonyl Butoxide 4% Shampoo (Rid)
      1. Mechanism: Neurotoxic to lice
      2. Apply Shampoo to dry hair and rinse in 10 minutes
      3. Requires second treatment in 9-10 days
  3. Medications used in resistant cases
    1. FDA approved use for Lice (prescription only)
      1. Permethrin 5% (Elimite)
      2. Topical Ivermectin (Sklice)
        1. Mechanism: Neurotoxic to lice
        2. Avoid under age 6 months old
        3. Single application is effective
        4. Apply to dry hair and scalp, leave on for 10 min, then rinse
        5. No repeat dosing needed
        6. Disadvantages: Expensive ($360 per tube in 2019), local inflammation, eye irritation
      3. Natroba (Spinosad) 0.9%
        1. Mechanism: Neurotoxic to lice
        2. Avoid under age 4 years old
        3. Apply to dry hair, leave on for 10 minutes and rinse
        4. Single application is effective (but may repeat in 9-10 days if lice are still present)
        5. Disadvantages: Expensive ($200-280 per bottle in 2019)
        6. Lice eradication rate (85%) is twice that of Permethrin
          1. Best efficacy is with nit combing
          2. Stough (2009) Pediatrics 124(3): e389-95 [PubMed]
      4. Abametapir (Xeglyze)
        1. FDA approved in 2022
        2. Single application to dry hair, coating all hair and massaging into scalp
        3. Leave on hair for 10 minutes and then rinse with warm water, avoiding any contact with eyes
        4. Approved for age 6 months and older (possible systemic effects in younger infants)
        5. Adverse reactions include local scalp reactions in <5% of patients
        6. Inhibits CYP3A4, CYP3B6 and CYP1A2
          1. Risk of increased levels of drugs metabolized by these Cytochrome P450 enzymes
        7. References
          1. Sunder (2022) Am Fam Physician 106(1): 91-2 [PubMed]
      5. Ulesfia (Benzyl Alcohol 5% lotion)
        1. Mechanism: Suffocates lice
        2. Avoid under age 6 months old
        3. May be used in pregnancy and Lactation
        4. Apply to dry hair, leave on for 10 minutes and then rinse
        5. Apply now and in 7 days
        6. Requires nit combing (see below)
        7. Comparable efficacy to first-line lice treatments at 3 times the cost (>$450 per bottle in 2019)
          1. Even more expensive in long hair
      6. Dimethicone Solution (Nix Ultra, Lice MD)
        1. Mechanism: Suffocates lice
        2. Avoid in children under age 2 years
        3. Spray all over dry hair and massage until wet, let sit 30 min, comb into hair and leave overnight
        4. Wash out and use lice comb
        5. Repeat in 8-10 days
      7. Isopropyl myristate solution (Resultz)
        1. Mechanism: Dissolves lice exoskeleton
        2. FDA approved in 2017, but not yet available in U.S. as of 2019
        3. Avoid in children under age 4 years
        4. Apply to dry hair and scalp, leave on for 10 min, then rinse in warm water
        5. Repeat in 8-10 days
    2. Not FDA approved for Lice
      1. Ivermectin (Stromectol)
        1. Mechanism: Neurotoxic to lice
        2. Avoid in pregnancy, Lactation and in children weighing under 15 kg (33 lb)
        3. Initial Dose: 200 mcg/kg orally now and in 7 days
        4. Highly effective (95% eradication rate) and inexpensive
          1. Consider as second-line agent for refractory cases
          2. Chosidow (2010) N Engl J Med 362(10): 896-905 [PubMed]
      2. Dry-On Suffocation-based Pediculicide (Nuvo Lotion)
        1. Mechanism: Suffocates lice
        2. Nuvo-Lotion is identical to Cetaphil (OTC)
        3. Applied to hair and hair blow-dried
        4. Limited and low quality evidence of benefit
        5. Nuvo Protocol Resource
        6. Pearlman (2004) Pediatrics 114(3): e275-9 [PubMed]
  4. Medications in cases refractory to measures above (higher toxicity risk)
    1. Malathion (Ovide) 0.5%
      1. Mechanism: Neurotoxic to lice
      2. Avoid under age 6 years old (some use down to age 2 years)
      3. Apply to dry hair, air dry, and Shampoo off in 8-12 hours
      4. Use lice comb after application
      5. Single application is effective (but may repeat in 9-10 days if lice are still present)
      6. Disadvantages
        1. Expensive ($150-270 in 2019)
        2. Flammable (do not use with hair dryer or open flame)
    2. Lindane (Gamma Benzene Hexachloride) 1%
      1. Not recommended due to neurotoxicity (Seizure risk, especially in children) and Aplastic Anemia risk
      2. Use only in adults >50 kg (not elderly) and only when other, safer options have been exhausted
  5. Specific Approaches
    1. Head Lice
      1. See Below
      2. Clean hats, brushes and combs, linen and bedding at high Temperature
      3. Examine family members and close school contacts and treat if lice identified
      4. Children should not miss school for lice infestation (per AAP)
    2. Body Lice
      1. Same pediculicidal agents used for Head Lice (see first-line and second-line agents as below)
      2. Normal hygiene
      3. Clean hats, brushes and combs, linen and bedding at high Temperature (see above)
      4. Treat partner contacts within prior 3 months
    3. Pediculosis Pubis (Genital Lice)
      1. Permethrin 1% cream
        1. Apply to pubic and perianal regions as well as thighs and axillae
        2. Wash off in 10 minutes
        3. Consider repeat application in 1 week
      2. Screen for other Sexually Transmitted Diseases
      3. Treat sexual partners within last month
      4. Wash clothing and bedding as described above (environmental measures)
    4. Pediculosis Ciliaris (eyelash lice, same lice as Pubic Lice)
      1. Apply occlusive ointment (e.g. vaseline petrolatum) to Eyelid margins twice daily for 8-10 days
      2. Remove lice using mechanical removal techniques as below
      3. Consider Ivermectin 200 mcg/kg orally now and again in 1 week
  • Management
  • Protocol for Head Lice
  1. Identify presence of live lice, not simply nits (See signs above)
    1. Treat only if live lice are identified
  2. Use one of medications listed below (see above for descriptions of these agents)
    1. First Line
      1. Permethrin 1% (Nix) cream rinse
      2. Pyrethrins with Piperonyl Butoxide (Rid)
    2. Second Line
      1. Malathion 0.5% topically (FDA approved) or
      2. Ivermectin (not FDA approved) or
      3. Permethrin 5% Cream
    3. Third Line
      1. Consider re-exposure instead of resistance
      2. Reinforce nit removal (see below)
      3. See numerous treatment options as above
      4. Option 1: Combination therapy
        1. Trimethoprim-Sulfamethoxazole (Bactrim) x10 days
        2. Permethrin 1% (2 applications, 7-10 days apart)
      5. Option 2: Monotherapy with one of agents below
        1. Malathion (Ovide) 0.5% topically (FDA approved)
        2. Ivermectin (not FDA approved)
  3. Remove nits with fine-toothed comb (mechanical nit removal)
    1. Required regardless of medication used (none are 100% effective without nit removal)
    2. Technique
      1. Use regular comb or brush first to detangle hair
      2. Wet hair and apply regular hair conditioner
      3. Comb hair from root to tip with lice comb
      4. Rinse out hair conditioner
      5. Comb hair again from root to tip with lice comb
    3. Adjuncts
      1. Regular hair conditioner appears to be most effective compared with vinegar, formic acid, almond oil
      2. No evidence of better efficacy with an electronic comb compared with a lice comb
    4. Use fine-toothed nit comb (e.g. Licemeister Comb)
    5. If only using wet-combing alone (without medications)
      1. Repeat nit removal every 2-3 days for 2-3 weeks until no lice are seen
      2. Efficacy of wet combing alone without medication: 47-75%
  4. Reapply medication and remove nits in 7-10 days
  5. Recheck hair for nits over 72 hours
  • Management
  • Exposure
  1. Risk of transmission is low with casual contact
    1. Contacts have been exposed >1 month at diagnosis
    2. Children may attend school after treatment
    3. Nits are not a contraindication for school attendance
    4. Simply avoid direct head to head contact and do not share hats, combs or pillows
  2. Avoid embarrassing child
    1. Notify child's parents immediately
    2. Keep diagnosis confidential
    3. Ensure prompt treatment and avoid missing school
  3. Treatment indications
    1. Check household exposures
      1. Live lice or eggs seen within 1 cm of scalp
      2. Treat family members who share same bed as child
    2. Head Lice screening programs are not recommended
      1. Do not reduce Head Lice Incidence
      2. Not cost effective
  • Precautions
  • Alternative therapies that do not work well and are not recommended
  1. Mechanical "Bug-busting" (wet combing hair for 2 weeks)
  2. Petroleum jelly, Mayonaise, or kerosene for suffocation of lice (no evidence, messy, toxicity)
  3. Head shaving has only brief effect
  4. Homeopathic Products (no evidence of benefit)
  5. Essential Oils or tea tree oil (no evidence of benefit and risk of Contact Dermatitis)
  • Resources
  1. National Pediculosis Association
    2. Phone: 888-542-3634
  2. Lice Fighting Center (Commercial site)