Lice

Lice are tiny parasitic insects that infest human hair and skin, feeding on blood and causing intense itching. Three types affect humans: head lice, body lice, and pubic lice. While not dangerous, lice infestations are highly contagious and require prompt treatment.

Overview

Lice infestations, medically known as pediculosis, are one of the most common parasitic infestations worldwide. These tiny, wingless insects are obligate human parasites, meaning they can only survive by feeding on human blood. Each type of louse is adapted to live in specific areas of the human body and cannot survive long away from their human host. Despite common misconceptions, lice infestations have nothing to do with personal hygiene or cleanliness.

The three types of lice that infest humans are distinct species: Pediculus humanus capitis (head louse), Pediculus humanus corporis (body louse), and Pthirus pubis (pubic or crab louse). Head lice are the most common, particularly among school-aged children, affecting millions annually. Body lice are less common in developed countries and are associated with poor living conditions and lack of access to clean clothing. Pubic lice are typically transmitted through sexual contact and have become less common in recent years.

Lice are highly specialized parasites that have evolved alongside humans for thousands of years. They cannot jump or fly but spread through direct contact or, less commonly, through shared personal items. While lice do not transmit diseases in most cases (except body lice, which can carry certain bacterial infections), the intense itching they cause can lead to secondary bacterial infections from scratching. Understanding the biology and behavior of lice is crucial for effective treatment and prevention of reinfestation.

Symptoms

Lice infestation symptoms vary depending on the type of lice and the individual's sensitivity to louse saliva. Some people may have lice for weeks before developing symptoms, while others react quickly. The primary symptom is itching caused by an allergic reaction to louse saliva.

Head Lice Symptoms

  • Intense itching of the scalp
  • Feeling of something moving in the hair
  • Visible nits (eggs) attached to hair shafts
  • Small red bumps on scalp, neck, and shoulders
  • Difficulty sleeping (lice are most active at night)
  • Irritability and difficulty concentrating
  • Swollen lymph nodes behind ears or neck

Body Lice Symptoms

  • Intense itching, especially at night
  • Red bumps and scratch marks on body
  • Thickened or darkened skin (with chronic infestation)
  • Visible lice or nits in clothing seams
  • Secondary bacterial infections from scratching
  • General malaise and irritability

Pubic Lice Symptoms

  • Intense itching in genital area
  • Visible lice or nits in pubic hair
  • Blue-gray spots (maculae ceruleae) on skin
  • Dark brown or rust-colored specks in underwear
  • Mild fever (occasionally)
  • Irritability and discomfort

Secondary Symptoms

Complications from scratching and secondary infections may cause:

  • Bacterial skin infections (impetigo)
  • Swollen lymph nodes
  • Excoriation (scratch marks) and scarring
  • Sleep disturbances leading to daytime fatigue
  • Social embarrassment and psychological distress
  • In severe cases with body lice: fever, headache, and rash

Causes

Lice infestations are caused by specific species of parasitic insects that have adapted to live on humans. Understanding their biology and transmission methods is essential for effective treatment and prevention.

The Parasites

  • Head Lice (Pediculus humanus capitis)
    • Size: 2-3 mm (adult), sesame seed-sized
    • Color: Tan to grayish-white
    • Lifespan: Up to 30 days on a host
    • Eggs (nits): Laid close to scalp, hatch in 7-10 days
    • Cannot survive more than 1-2 days off the host
  • Body Lice (Pediculus humanus corporis)
    • Slightly larger than head lice
    • Live in clothing, move to skin to feed
    • Can survive up to 10 days in clothing
    • Can transmit diseases (typhus, trench fever, relapsing fever)
  • Pubic Lice (Pthirus pubis)
    • Size: 1.1-1.8 mm, crab-like appearance
    • Shorter, broader body with large claws
    • Attach to coarse body hair
    • Move very slowly compared to other lice

Transmission Methods

Head Lice Transmission

  • Direct head-to-head contact (most common)
  • Sharing personal items: combs, brushes, hair accessories
  • Sharing clothing: hats, scarves, coats
  • Lying on contaminated bedding or furniture (less common)
  • NOT spread by jumping or flying

Body Lice Transmission

  • Sharing contaminated clothing or bedding
  • Living in crowded, unsanitary conditions
  • Lack of access to clean clothing and regular bathing
  • Common in homeless populations, refugees, natural disasters

Pubic Lice Transmission

  • Sexual contact (most common)
  • Close personal contact
  • Sharing contaminated towels or bedding (rare)
  • Can spread to other coarse hair (beard, eyebrows, eyelashes)

Life Cycle

Understanding the lice life cycle is crucial for treatment:

  1. Egg (Nit) Stage: 6-9 days, firmly attached to hair shaft
  2. Nymph Stage: 9-12 days, three molts to become adult
  3. Adult Stage: Can live 30 days, females lay 6-10 eggs daily

Why Infestations Persist

  • Resistance to over-the-counter treatments
  • Incomplete treatment or missed follow-up treatments
  • Reinfestation from untreated contacts
  • Not treating the environment properly
  • Misdiagnosis (mistaking dandruff or debris for nits)

Risk Factors

Certain factors increase the likelihood of lice infestation. Understanding these risks helps in prevention and early detection of infestations.

Age and Demographics

Head lice most commonly affect children aged 3-11 years and their families. Girls are more frequently affected than boys, possibly due to more frequent head-to-head contact during play. Adults who work with children are also at increased risk.

Living Conditions

Crowded living situations increase transmission risk. This includes dormitories, shelters, refugee camps, and households with many children. Body lice specifically affect those without regular access to clean clothing and bathing facilities.

Social Activities

Activities involving close physical contact increase risk. This includes contact sports, sleepovers, camps, and play dates. Sharing personal items like hair accessories, headphones, or helmets also increases risk.

Hair Characteristics

Contrary to popular belief, lice prefer clean hair as it's easier to attach eggs. Hair length, thickness, or cleanliness doesn't prevent infestation. All hair types and textures can be affected, though some studies suggest certain hair types may be less susceptible.

Seasonal Patterns

Head lice infestations often peak after school starts in fall and after winter and spring breaks when children have been in close contact. Summer camps also see increased transmission.

Previous Infestation

Having lice before doesn't provide immunity. In fact, those who've had lice may be at higher risk for reinfestation if they're in environments where lice are common or if close contacts aren't properly treated.

Diagnosis

Accurate diagnosis of lice infestation is crucial for appropriate treatment. Many conditions can mimic lice, and misdiagnosis can lead to unnecessary treatment and continued transmission if true infestation is missed.

Visual Inspection

What to Look For

  • Live lice: Adult lice move quickly and avoid light
  • Nymphs: Smaller, translucent versions of adults
  • Nits: Oval eggs firmly attached to hair shaft near scalp
  • Nit casings: Empty shells after hatching (white/clear)
  • Fecal spots: Dark specks on scalp or in hair

Inspection Technique

  • Use bright light and magnifying glass
  • Part hair systematically in small sections
  • Pay special attention to behind ears and nape of neck
  • Wet combing is more effective than dry inspection
  • Use fine-toothed lice comb on wet, conditioned hair

Differentiating Active Infestation

  • Active infestation: Live lice or viable nits within 1⁄4 inch of scalp
  • Past infestation: Only empty nit casings or nits far from scalp
  • Viable nits: Tan/brown color, plump appearance
  • Non-viable nits: White/clear, flat appearance

Differential Diagnosis

Conditions that may be mistaken for lice:

  • Dandruff: Flakes easily removed, not attached to hair
  • Hair casts: Cylindrical, slide easily along hair
  • Seborrheic dermatitis: Greasy scales, inflammation
  • Hair product residue: Irregular shape, easily removed
  • Psoriasis: Thick, silvery scales on scalp
  • Eczema: Red, inflamed patches with scaling

Diagnostic Tools

  • Lice comb: Fine-toothed metal comb (tooth spacing 0.2-0.3mm)
  • Magnification: Handheld magnifier or dermatoscope
  • Wood's lamp: May help visualize nits (limited use)
  • Microscopy: Definitive identification if needed
  • Tape test: Clear tape to collect specimens

Documentation

Important to document for treatment monitoring:

  • Number and location of live lice found
  • Presence and location of nits
  • Symptoms and their duration
  • Previous treatments tried
  • Household and close contacts

Treatment Options

Effective lice treatment requires killing both live lice and their eggs, preventing reinfestation, and treating all affected individuals simultaneously. Treatment approaches vary by lice type and may require multiple applications.

Over-the-Counter Treatments

Pyrethrin-Based Products

  • Derived from chrysanthemum flowers
  • Examples: RID, A-200, Pronto
  • Apply to dry hair, leave 10 minutes
  • Requires second treatment in 9-10 days
  • Not ovicidal (doesn't kill all eggs)
  • Contraindicated in ragweed allergy

Permethrin 1% (Nix)

  • Synthetic pyrethroid
  • More effective than pyrethrins
  • Some residual activity (up to 2 weeks)
  • Apply to damp hair, leave 10 minutes
  • May require second treatment
  • Increasing resistance reported

Prescription Treatments

Topical Prescriptions

  • Malathion 0.5% (Ovide):
    • Organophosphate, highly effective
    • Apply to dry hair, leave 8-12 hours
    • Flammable - avoid heat sources
  • Benzyl alcohol 5% (Ulesfia):
    • Suffocates lice, no neurotoxic action
    • Not ovicidal, requires repeat treatment
    • Safe for ages 6 months and up
  • Spinosad 0.9% (Natroba):
    • Derived from soil bacteria
    • Single treatment often effective
    • Ovicidal properties
  • Ivermectin 0.5% lotion (Sklice):
    • Single application usually sufficient
    • Apply to dry hair, rinse after 10 minutes
    • For ages 6 months and older

Oral Medications

  • Oral Ivermectin:
    • For resistant cases or multiple infestations
    • Two doses, 7-10 days apart
    • Not FDA approved for lice (off-label use)
    • Weight-based dosing
  • Trimethoprim-sulfamethoxazole:
    • Sometimes used with permethrin
    • May enhance pediculicide activity

Non-Pesticide Treatments

  • Wet combing (Bug Busting):
    • Systematic combing every 3-4 days for 2 weeks
    • Use conditioner and fine-toothed metal comb
    • Time-intensive but avoids pesticides
  • Suffocation methods:
    • Petroleum jelly, mayonnaise, olive oil
    • Limited evidence of effectiveness
    • Must be left on 8+ hours
  • Heat treatment:
    • Professional heated air devices (AirAllé)
    • Not regular hair dryers (can spread lice)
  • Essential oils:
    • Tea tree, lavender, eucalyptus
    • Limited evidence, potential toxicity

Environmental Treatment

  • Clothing and bedding:
    • Machine wash in hot water (130°F/54°C)
    • Dry on high heat for 20+ minutes
    • Seal non-washables in plastic bags for 2 weeks
  • Personal items:
    • Soak combs/brushes in hot water (130°F) for 10 minutes
    • Or freeze items for 48 hours
  • Household:
    • Vacuum carpets and furniture
    • No need for pesticide sprays
    • Focus on items used in past 48 hours

Treatment by Lice Type

  • Head lice: Follow standard treatment protocols above
  • Body lice:
    • Improve hygiene and living conditions
    • Regular bathing and clean clothes
    • Treat clothing and bedding
    • Rarely need body treatment
  • Pubic lice:
    • Permethrin or pyrethrin to affected areas
    • Treat sexual partners simultaneously
    • May need different treatment for eyelashes
    • Screen for other STIs

Prevention

While complete prevention of lice exposure may not be possible, especially for children, various strategies can significantly reduce the risk of infestation and prevent spread within families and communities.

Primary Prevention

  • Avoid head-to-head contact: The most important prevention measure
  • Don't share personal items:
    • Hair brushes, combs, and accessories
    • Hats, scarves, and hooded clothing
    • Headphones and helmets
    • Towels and pillows
  • Personal space awareness: Teach children about personal space
  • Hair management: Long hair in braids or buns during outbreaks

Early Detection

  • Regular checks: Weekly during peak seasons
  • Know the signs: Excessive scratching, difficulty sleeping
  • Check after exposure: Sleepovers, camps, close contact
  • Educate children: Report itching or "tickling" sensations

School and Community Measures

  • No-nit policies: Controversial, not recommended by AAP
  • Education programs: For parents, teachers, and children
  • Screening programs: During outbreaks
  • Reduce stigma: Emphasize lice prefer clean hair
  • Communication: Alert close contacts when cases identified

Home Environment

  • Separate storage: Individual cubbies or hooks for belongings
  • Regular cleaning: But avoid excessive measures
  • Teach good habits: Not sharing personal items
  • Monitor siblings: Check all family members if one has lice

Prevention Products

  • Repellent shampoos: Limited evidence of effectiveness
  • Essential oil products: May have some deterrent effect
  • Leave-in sprays: Not proven to prevent infestation
  • Regular shampoo: No preventive benefit

When to See a Doctor

While many lice infestations can be treated at home, certain situations require professional medical evaluation and treatment.

Seek Medical Care For

  • Treatment failure after two properly applied OTC treatments
  • Signs of secondary skin infection (pus, spreading redness, fever)
  • Lice in eyebrows or eyelashes
  • Severe scratching leading to open wounds
  • Allergic reactions to treatments
  • Infestations in infants under 2 months
  • Pregnant or breastfeeding women
  • People with compromised immune systems

Professional Treatment Needed

  • Resistant lice not responding to OTC treatments
  • Multiple family members with recurring infestations
  • Uncertainty about diagnosis
  • Body lice infestation (may indicate other health issues)
  • Severe psychological distress from infestation

What to Expect at Doctor Visit

  • Confirmation of diagnosis through examination
  • Prescription for stronger pediculicides if needed
  • Treatment of secondary infections
  • Guidance on environmental cleaning
  • Family treatment recommendations

Related Conditions

Other Parasitic Conditions

Scalp Conditions

Related Symptoms

References

  1. Devore CD, Schutze GE. Head Lice. Pediatrics. 2015;135(5):e1355-e1365.
  2. CDC. Parasites - Lice. Centers for Disease Control and Prevention. Updated 2023.
  3. Feldmeier H. Pediculosis capitis: new insights into epidemiology, diagnosis and treatment. Eur J Clin Microbiol Infect Dis. 2012;31(9):2105-2110.
  4. Burgess IF. Current treatments for pediculosis capitis. Curr Opin Infect Dis. 2009;22(2):131-136.
  5. American Academy of Pediatrics. Red Book: 2021-2024 Report of the Committee on Infectious Diseases. 32nd ed.

Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.