What are head lice in humans?

Understanding Head Lice

What are Head Lice?

Definition and Characteristics

Head lice (Pediculus humanus capitis) are obligate ectoparasitic insects that inhabit the human scalp and feed exclusively on blood from the scalp skin.

Adults measure 2–4 mm in length, are gray‑white to brown, lack wings, and possess six legs ending in clawed tarsi that grasp hair shafts. The head is compact, with a dorsoventral flattening that facilitates movement through dense hair. Eyes are reduced to simple ocelli, and antennae are short, bearing sensory receptors for temperature and carbon‑dioxide.

The life cycle comprises three stages:

Egg (nit): oval, 0.8 mm long, firmly attached to the hair shaft 1–2 cm from the scalp; incubation lasts 7–10 days.
Nymph: three successive molts occur over 9–12 days; each instar resembles a miniature adult but is incapable of reproduction.
Adult: reaches sexual maturity after the final molt; lifespan on a host ranges from 30 to 40 days, during which a female may lay 6–10 eggs per day.

Head lice crawl rather than jump or fly, moving primarily along hair shafts toward the scalp where temperature and moisture are optimal. They survive only a few hours off the human host, reflecting an obligate dependence on the scalp environment for feeding, reproduction, and development.

Life Cycle of Head Lice

Head lice (Pediculus humanus capitis) complete their development on a human scalp, progressing through three distinct stages: egg, nymph, and adult.

The female deposits oval eggs, called nits, firmly attached to hair shafts within 1 mm of the scalp. Each nit measures about 0.8 mm and requires 7–10 days to hatch under optimal temperature (30–32 °C) and humidity conditions.

Upon emergence, the newly hatched nymph resembles a miniature adult but lacks reproductive capacity. Nymphs undergo three successive molts, each lasting approximately 3–4 days. After the final molt, the insect reaches full maturity.

Adult lice measure 2–3 mm, survive up to 30 days on the host, and feed exclusively on blood several times daily. Females lay 5–10 eggs per day, replenishing the population and sustaining the infestation.

The entire cycle—from egg to reproducing adult—spans roughly 2–3 weeks, allowing rapid expansion when untreated. Continuous monitoring and timely intervention interrupt this progression and prevent resurgence.

How Head Lice Spread

Common Transmission Methods

Head lice are obligate ectoparasites that survive on the human scalp by feeding on blood. Their spread relies on physical contact that moves adult insects or viable eggs (nits) from one host to another.

Direct head‑to‑head contact during play, sports, or close social interaction.
Sharing personal items such as combs, brushes, hair ties, hats, or helmets.
Contact with contaminated fabrics, including pillows, blankets, clothing, or upholstered furniture.
Indirect transfer via objects that have recently contacted an infested scalp, though viability decreases rapidly on dry surfaces.

Transmission requires the lice or nits to reach a suitable environment on a new host’s hair within a few days; the insects cannot travel through the air or survive long periods away from a scalp.

Risk Factors for Infestation

Head lice (Pediculus humanus capitis) are obligate ectoparasites that inhabit the scalp, feeding on blood and laying eggs (nits) attached to hair shafts. Infestation occurs when viable lice are transferred from one host to another, typically through direct head‑to‑head contact.

Close physical contact in schools, daycare centers, or sports teams
Shared personal items such as combs, hats, helmets, or headphones
Crowded living conditions, including shelters, dormitories, and military barracks
Inadequate hygiene practices, especially infrequent hair washing or limited access to clean bedding
Recent outbreaks within a community or household, indicating a high local prevalence
Age group 3–11 years, reflecting increased social interaction and group activities

These factors elevate the probability of lice transfer and support rapid spread within susceptible populations. Mitigation strategies focus on reducing contact opportunities, avoiding the exchange of personal grooming accessories, and maintaining regular inspection of hair in high‑risk environments.

Symptoms and Diagnosis

Recognizing an Infestation

Common Symptoms

Head lice are tiny, wing‑less insects that live on the scalp and feed on blood. Infestation produces a recognizable set of clinical signs.

Persistent itching, especially around the ears and nape of the neck, caused by an allergic reaction to saliva.
Visible nits (lice eggs) attached to hair shafts within 1 cm of the scalp; they appear as tiny, white or yellowish specks.
Live lice moving quickly across the scalp or clinging to hair strands; they may be seen on close inspection.
Small red or pink spots on the scalp where bites have occurred; these may become irritated or develop a crust.
Secondary skin irritation or infection resulting from excessive scratching.

Symptoms typically emerge within 4–6 weeks after initial contact, persist until treatment, and may fluctuate with the lice life cycle. Absence of these signs generally indicates no active infestation.

Visual Detection

Visual detection of pediculosis capitis relies on direct observation of live insects, eggs, and characteristic skin changes on the scalp and hair. The practitioner examines the hair shaft from the scalp outward, using a fine-toothed comb or magnifying lens to separate strands and expose hidden parasites.

Key indicators include:

Live lice: gray‑brown, wingless insects measuring 2–4 mm, moving rapidly when disturbed.
Nits: oval, translucent or white eggs firmly attached to the side of the hair shaft, typically within 1 cm of the scalp.
Viable nits: eggs with a visible embryo or a darkened dot indicating development.
Brownish specks: fecal matter deposited near the hair root, often mistaken for dandruff.

Effective visual assessment follows a systematic protocol:

Separate hair into sections of 2–3 cm.
Comb each section with a fine-toothed (0.2 mm) lice comb, starting at the scalp and moving outward.
Inspect the comb teeth and hair under at least 10× magnification.
Record the presence, location, and developmental stage of each finding.
Repeat the process after a 7‑day interval to verify treatment efficacy.

Accurate visual detection distinguishes live lice from nits, preventing misdiagnosis and guiding appropriate management.

Professional Diagnosis

Examination Procedures

Head lice infestations in humans are diagnosed through a systematic visual and tactile examination. The clinician begins by obtaining a brief history of symptoms such as itching, scalp irritation, or recent exposure to infested individuals. This information guides the focus of the inspection.

The primary assessment consists of a thorough scalp survey. The examiner separates hair strands with a fine-toothed comb, preferably a lice comb with 0.2 mm spacing, while the scalp is illuminated by a bright light source. The comb is run from the scalp outward, and each pass is examined for live insects, immature forms, or attached eggs. Detection of viable lice confirms active infestation; identification of viable nits attached within 1 cm of the scalp indicates recent or ongoing colonization.

If visual findings are ambiguous, supplemental techniques may be employed:

Wet-mount microscopy: a few hair shafts are placed on a slide with saline solution, covered, and examined under a compound microscope at 10–40× magnification to reveal subtle morphological details.
Dermatoscopy: a handheld dermatoscope provides polarized illumination and 10–30× magnification, allowing rapid assessment of lice movement and egg placement.
Adhesive tape test: clear adhesive tape is pressed to the scalp, then examined under a microscope to capture any detached lice or nits.

Environmental assessment follows the clinical examination. The practitioner inspects personal items (hats, hairbrushes, bedding) for signs of infestation, documenting any potential sources of re‑contamination.

Documentation includes the number and developmental stage of lice observed, the location and condition of nits, and any secondary skin lesions. This record supports treatment planning and enables follow‑up evaluation of therapeutic efficacy.

Differentiating from Other Conditions

Head lice infestation in humans presents with specific clinical signs that allow clear separation from other scalp disorders. Live insects or their nits attached to hair shafts are the most reliable indicator. Nits are firmly cemented near the scalp, often at the base of hair strands, and can be removed only with fine forceps. Adult lice are visible to the naked eye as small, wingless insects moving slowly across the scalp.

Key distinguishing features include:

Presence of viable lice or nits versus shed skin scales; lice are motile, whereas dandruff consists of loose, non‑adherent flakes.
Intense itching that intensifies after periods of inactivity (e.g., overnight); allergic dermatitis may cause itching but typically lacks the pattern of nocturnal exacerbation.
Localized erythema and small punctate lesions caused by lice bites; fungal infections such as tinea capitis produce circular, scaly patches with possible hair loss.
Absence of widespread scalp inflammation or silvery scales, which are characteristic of psoriasis or seborrheic dermatitis.
Lack of systemic symptoms such as fever or lymphadenopathy, distinguishing infestation from secondary bacterial infection of the scalp.

Diagnostic confirmation relies on direct visualization of live lice or viable nits. Microscopic examination of collected specimens can further verify species identification and rule out mimicking conditions.

Treatment Options

Over-the-Counter Remedies

Types of Products

Head lice are obligate ectoparasites that live on the human scalp, feed on blood, and lay eggs (nits) attached to hair shafts. Effective control relies on products designed to eliminate both adult insects and their eggs.

Synthetic neurotoxic pediculicides – formulations containing permethrin, pyrethrin, or carbaryl; act on the nervous system of the lice, providing rapid knock‑down.
Silicone‑based agents – dimethicone or cyclomethicone liquids that coat the insect, obstructing respiration and causing desiccation; effective against resistant strains.
Plant‑derived preparations – essential oil blends (e.g., tea tree, eucalyptus, neem) formulated in shampoos or sprays; possess insecticidal or repellent properties, often combined with surfactants to improve penetration.
Prescription oral medications – ivermectin or nitazoxanide tablets prescribed for severe infestations; act systemically to disrupt parasite metabolism.
Mechanical removal tools – fine‑toothed nit combs made of stainless steel or plastic; physically extract lice and nits when used with a conditioning agent.
Combination products – dual‑action formulas that include a pediculicide plus a surfactant or silicone; aim to kill insects and loosen egg attachments simultaneously.

Selection criteria include resistance patterns in the local lice population, age and health status of the individual, and potential skin sensitivities. Application must follow label instructions regarding contact time, repeat treatment intervals, and thorough combing to prevent re‑infestation.

Application Instructions

The following instructions detail the correct use of a pediculicide product to eliminate human head‑lice infestations.

Verify the product’s expiration date; do not apply expired medication.
Read the safety information on the label, noting any contraindications for children under two years or individuals with known allergies.
Separate the affected person’s hair from untreated hair using a clean comb or hair clips.
Apply the liquid or lotion evenly to dry scalp, covering the entire hair length from the crown to the tips.
Massage gently for the time specified on the label, typically 10 minutes, to ensure penetration of the active ingredient.
Rinse thoroughly with lukewarm water; avoid hot water that may degrade the formulation.
After drying, run a fine‑toothed nit comb through the hair in sections, removing dead insects and eggs.
Repeat the treatment after seven days to eradicate any newly hatched lice that survived the first application.
Clean all personal items (combs, hats, pillowcases) by washing in hot water (≥ 60 °C) or sealing in a plastic bag for two weeks.

Adherence to each step maximizes efficacy and minimizes the risk of reinfestation.

Prescription Medications

When to Consult a Doctor

Head lice infestations that persist despite appropriate over‑the‑counter therapy, cause intense discomfort, or lead to secondary skin infection require professional evaluation. If a person experiences any of the following, a medical appointment is advisable:

Persistent itching for more than two weeks, especially if it interferes with sleep or daily activities.
Visible sores, crusted lesions, or pus on the scalp, indicating bacterial infection.
Fever, swollen lymph nodes, or a rash extending beyond the scalp.
Infestation in infants younger than six months, children under two years, or pregnant individuals, for whom standard treatments may be unsafe.
Recurrent infestations after a complete treatment cycle, suggesting resistance or reinfestation from close contacts.
Uncertainty whether the observed insects are lice or another parasitic or dermatological condition.

A clinician can confirm the diagnosis, prescribe prescription‑strength pediculicides, address complications, and provide guidance on preventing further spread within households or schools. Early professional intervention reduces the risk of prolonged infestation and associated health issues.

Available Treatments

Head lice infestations affect the scalp and hair, requiring prompt eradication to prevent spread. Effective management combines chemical agents, mechanical removal, and environmental control.

Common chemical treatments include:

Permethrin 1% lotion applied to dry hair, left for 10 minutes, then rinsed; repeat after 7–10 days.
Pyrethrin‑based products mixed with piperonyl‑butoxide, used similarly to permethrin.
Dimethicone (silicone‑based) lotion that suffocates lice without neurotoxic action; typically left for 8 hours before washing.
Ivermectin 0.5% lotion applied for 10 minutes, then rinsed; a second application after one week addresses emerging nymphs.
Malathion 0.5% shampoo, left for 8–12 hours; reserved for cases with known resistance to other agents.

Mechanical methods focus on direct removal:

Fine‑toothed nit combs used on wet, conditioned hair; comb through each section repeatedly for 10–15 minutes, followed by thorough cleaning of the comb after each pass.
Manual extraction with tweezers for visible nits; effective only when infestation is light.

Environmental measures reduce reinfestation risk:

Washing bedding, clothing, and towels in water ≥ 60 °C or dry cleaning; items unable to be laundered should be sealed in plastic bags for two weeks.
Vacuuming carpets, furniture, and car seats to capture stray lice.
Avoiding shared personal items such as hats, hairbrushes, and headphones.

Resistance to pyrethroids has increased globally; clinicians often prefer dimethicone or ivermectin for persistent cases. Treatment failure warrants confirmation of correct application, a second‑line agent, or combined chemical and mechanical approaches. Follow‑up examinations at 7–10 days after initial therapy verify eradication; residual live nits indicate the need for retreatment.

Non-Chemical Approaches

Manual Removal (Combing)

Manual removal of head lice relies on a fine‑toothed comb to separate insects and their eggs from hair shafts. The process begins with washing the scalp with a regular shampoo, rinsing thoroughly, and towel‑drying to a damp but not wet condition. Apply a generous amount of a water‑based conditioner or a specialized lice‑combing lotion to reduce friction and improve slide of the comb.

Using a metal or plastic nit comb with teeth spaced 0.2–0.3 mm, start at the scalp close to the roots. Pull the comb through a small section of hair, moving slowly toward the tips. After each pass, wipe the teeth on a white tissue or rinse under running water to expose any captured lice or nits. Repeat the action for every section, ensuring coverage of all areas, including behind the ears and at the nape.

A systematic schedule enhances success. Perform the combing session daily for seven consecutive days, then repeat after three days to catch any newly hatched nymphs. Record the number of live insects and nits removed each session; a decline to zero indicates effective control.

Advantages of this technique include absence of chemical exposure, immediate visual confirmation of removal, and suitability for individuals with sensitivities to insecticides. Limitations involve the time required—approximately 15–30 minutes per person—and the need for consistent repetition. Proper training reduces the risk of missing hidden nits, especially in dense or curly hair.

After the final session, wash all combs in hot, soapy water, disinfect with a 70 % alcohol solution, or place in a dishwasher if compatible. Launder clothing, bedding, and personal items on the hottest cycle safe for the fabric, or seal them in a plastic bag for 48 hours to starve any surviving lice. Maintaining these steps prevents re‑infestation and supports long‑term eradication.

Alternative Therapies

Head lice (Pediculus humanus capitis) are obligate ectoparasites that live on the scalp and feed on human blood. Adult insects measure 2–4 mm, reproduce rapidly, and spread through direct head‑to‑head contact or shared personal items. Infestation causes itching, secondary bacterial infection, and social discomfort.

Alternative therapies aim to eradicate lice without conventional insecticides. Effectiveness varies; clinical evidence supports some methods, while others rely on anecdotal reports.

Essential‑oil preparations – blends containing tea tree, lavender, peppermint, or neem oil applied to the scalp for 30–60 minutes, then rinsed. Laboratory studies demonstrate ovicidal activity at concentrations above 1 %. Proper dilution is essential to avoid skin irritation.
Heat‑based treatments – devices that deliver controlled infrared or hot‑air exposure at 45–55 °C for 10–15 minutes. Heat disrupts louse metabolism and kills nymphs and eggs. Safety protocols require protection of hair and scalp from burns.
Silicone‑based lotions – high‑viscosity silicone compounds coat hair shafts, suffocating insects and preventing egg hatching. Products such as dimethicone 4% have shown comparable cure rates to permethrin in randomized trials.
Vinegar or acidic rinses – solutions of 5–10% acetic acid applied for several minutes loosen the cement that attaches nits to hair. Effectiveness depends on thorough combing after treatment.
Mechanical removal – fine‑toothed nit combs used on wet, conditioned hair. Repeated combing at 2‑day intervals eliminates live lice and eggs when performed for a minimum of three sessions.

When selecting an alternative approach, consider the following criteria:

Evidence base – prioritize methods with peer‑reviewed studies or systematic reviews.
Safety profile – evaluate risk of dermatitis, allergic reaction, or thermal injury.
User compliance – choose regimens that can be consistently applied by caregivers or patients.
Resistance avoidance – non‑chemical options reduce the likelihood of resistance development in lice populations.

Combining two or more strategies, such as a silicone lotion followed by meticulous combing, often improves eradication rates. Monitoring for re‑infestation over a 2‑week period remains essential; any resurgence should prompt repeat treatment or consultation with a healthcare professional.

Prevention and Management

Preventing Reinfestation

Hygiene Practices

Head lice are tiny parasitic insects that live on the scalp, feeding on human blood and laying eggs (nits) attached to hair shafts. Infestation spreads through direct head-to-head contact or sharing of personal items such as combs, hats, and pillows.

Effective hygiene measures reduce the risk of transmission and support treatment:

Wash hair daily with a regular shampoo; after confirmed infestation, use a medicated lice shampoo according to the product label.
Comb wet hair with a fine-toothed nit comb, removing lice and nits before rinsing.
Disinfect personal grooming tools (combs, brushes, hair accessories) by soaking in hot water (≥ 130 °F) for at least 10 minutes.
Launder clothing, bedding, and towels used by the infested individual in hot water (≥ 130 °F) and dry on high heat for a minimum of 30 minutes.
Store unused items (hats, scarves) in sealed plastic bags for two weeks to ensure any hidden lice die.
Avoid sharing personal items that contact the scalp; provide each person with their own combs, hair accessories, and headwear.

Regular inspection of the scalp, especially after group activities, enables early detection. Prompt removal of lice and nits, combined with the practices above, limits spread and facilitates recovery.

Environmental Control

Head lice are obligate ectoparasites that inhabit the human scalp, lay eggs on hair shafts, and feed on blood. While the insects cannot survive more than 24–48 hours without a host, contaminated objects can facilitate rapid re‑infestation. Effective environmental control limits the pool of viable lice and reduces the likelihood of recurrence after treatment.

Control measures focus on eliminating viable insects and eggs from clothing, bedding, and personal items. Heat and thorough washing are the most reliable methods because lice and nits are destroyed at temperatures above 50 °C. Regular cleaning of the immediate surroundings removes stray insects that may have fallen from the head.

Wash all clothing, towels, and bed linens in hot water (≥60 °C) and dry on high heat for at least 30 minutes.
Seal non‑washable items (e.g., hats, scarves) in airtight plastic bags for two weeks, the maximum survival period for lice off the host.
Vacuum carpets, upholstered furniture, and car seats; discard vacuum bags or clean canisters immediately after use.
Clean combs, brushes, and hair accessories by soaking in hot water (≥50 °C) for 10 minutes or applying a lice‑specific spray.

Implement the above actions within 48 hours of confirming an infestation and repeat laundering of reusable items after a second treatment cycle. Maintaining a clean environment alongside direct head treatment significantly lowers the risk of persistent or secondary outbreaks.

Managing Infestations in Schools and Communities

Communication and Protocols

Head lice (Pediculus humanus capitis) are ectoparasites that live on the scalp and feed on blood. Effective management depends on clear communication among health professionals, caregivers, and affected individuals, as well as adherence to established protocols.

Accurate information exchange begins with clinical assessment. Practitioners confirm infestation through visual inspection of live insects or viable nits. They convey diagnosis using standardized terminology, avoiding ambiguous descriptors. Documentation includes patient age, severity, and previous treatment attempts, ensuring continuity of care.

Protocols guide response at multiple levels:

Immediate treatment: prescribe a pediculicide approved by regulatory agencies; specify dosage, application duration, and re‑treatment interval.
Environmental control: instruct caregivers to wash bedding, clothing, and personal items at ≥60 °C or seal them in airtight containers for two weeks.
Follow‑up: schedule a re‑examination 7–10 days post‑treatment to verify eradication; record any residual lice or nits.
Reporting: notify school or workplace health officers when cases exceed local thresholds; provide anonymized data for surveillance.

Communication channels include face‑to‑face counseling, written instructions, and electronic alerts. Health agencies disseminate guidelines through official bulletins and online portals, ensuring that updates reach practitioners promptly. Schools implement notification systems that inform parents of confirmed cases while preserving confidentiality.

Adherence to these communication practices and procedural steps reduces transmission, limits re‑infestation, and supports public‑health objectives.

Reducing Stigma

Head lice are small, wingless insects that live on the scalp and feed on human blood. Infestations occur when lice eggs (nits) hatch and the newly emerged nymphs multiply, causing itching and discomfort. The condition affects individuals of all ages, socioeconomic backgrounds, and cultural groups.

Stigma surrounding head‑lice infestations stems from misconceptions that the presence of lice reflects poor hygiene or personal neglect. This belief fuels embarrassment, social isolation, and delayed treatment, which can exacerbate the spread of the parasites. Reducing stigma requires clear communication, education, and supportive policies.

Practical measures to diminish stigma include:

Accurate public education: Distribute fact‑based materials that explain lice transmission, emphasize that infestation is unrelated to cleanliness, and outline effective treatment options.
School‑based protocols: Implement confidential screening and treatment programs, ensuring that affected students receive care without public identification.
Healthcare provider training: Equip clinicians with communication strategies that address patients’ concerns respectfully and avoid judgmental language.
Media guidelines: Encourage journalists and influencers to report on lice issues using neutral terminology, avoiding sensationalism or ridicule.
Community support networks: Establish peer groups or online forums where families can share experiences, obtain advice, and receive emotional encouragement.

By integrating factual information, confidential services, and empathetic outreach, communities can eliminate the shame associated with head‑lice infestations and promote prompt, effective management.

Long-Term Management

Monitoring and Follow-up

Monitoring and follow‑up are essential components of effective management of pediculosis capitis in humans. After an initial treatment, verification of eradication requires a systematic inspection of the scalp and hair at regular intervals. The first reassessment should occur 7 days post‑treatment, focusing on live lice, viable nits within 1 cm of the scalp, and signs of reinfestation. A second examination at 14 days confirms the absence of newly hatched lice, which emerge from any surviving eggs within that period.

Continued surveillance extends to the household and close contacts. Each family member should be inspected simultaneously, and any positive findings mandate immediate retreatment and environmental measures. Documentation of inspection dates, findings, and interventions creates a traceable record that guides future decisions and reduces the risk of recurrence.

When multiple cases appear in a community setting—schools, daycare centers, or camps—public health officials implement broader monitoring protocols:

Weekly screening of all participants for a minimum of three weeks.
Aggregated reporting of positive cases to a central registry.
Coordination of synchronized treatment campaigns to interrupt transmission cycles.

The effectiveness of follow‑up hinges on adherence to the schedule, thorough visual examination aided by a fine‑toothed comb, and prompt action upon detection of residual infestation. Consistent application of these steps minimizes the likelihood of persistent or recurrent pediculosis capitis.

Addressing Psychological Impact

Head lice infestations often trigger intense embarrassment, social withdrawal, and anxiety, especially among school‑age children and their caregivers. The visible presence of live insects or nits can lead to perceived loss of personal hygiene, causing feelings of shame and fear of judgment from peers and adults. Persistent worry about contagion may result in heightened stress levels and disrupt normal daily activities, such as attending school or work.

Effective mitigation of these psychological effects requires a combination of factual education, emotional support, and practical measures. Providing accurate information about transmission, treatment efficacy, and the non‑reflective nature of personal cleanliness reduces misconceptions that fuel stigma. Confidential counseling sessions allow individuals to express concerns and develop coping strategies, while reassurance from healthcare professionals strengthens confidence in the treatment plan. Open communication with teachers and employers ensures accommodations that prevent isolation and maintain routine participation.

Practical steps to alleviate distress:

Distribute clear, age‑appropriate pamphlets describing the biology of the parasite and the short‑term nature of the condition.
Offer private consultation with a mental‑health specialist to address anxiety or shame.
Encourage families to discuss the issue calmly, emphasizing that infestations are common and treatable.
Coordinate with educational institutions to implement discreet screening and treatment protocols, avoiding public identification of affected students.
Monitor progress through follow‑up appointments, reinforcing successful eradication and normalizing the experience.

By integrating factual clarification, emotional reassurance, and coordinated support, the negative mental impact of head‑lice infestations can be substantially reduced, allowing affected individuals to resume regular activities without undue psychological burden.