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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Pediculosis and insect-bite reactions

Dermatology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull

Overview

Confirm lice by finding live insects, distinguish head, body and pubic infestation from bite hypersensitivity, coordinate contact and environmental measures, and identify anaphylaxis, infection, tick and safeguarding concerns.

Examine wet-combed hair in good light, especially behind ears and nape, and distinguish a live louse from adherent debris. Ask about treatment product, exact application and reinfestation before calling resistance. Avoid stigma: head lice affect clean hair and all social groups.

For bites, map exposed versus covered sites, puncta, crops and household pattern and ask about pets, beds, travel, outdoor and tick exposure. Papules can look red, violet or brown; swelling, central punctum and distribution remain useful across skin tones. Environmental eradication should target a confirmed source rather than indiscriminate insecticide spraying.

Pubic or body lice changes context. Offer confidential sexual-health assessment for pubic lice and safeguarding by age and circumstances. Body lice may signal lack of laundry access and deserves practical support. A tick still attached should be removed promptly with fine-tipped forceps close to skin, followed by symptom safety-netting rather than routine antibiotics for every bite.

Key points

  • Diagnose head lice only by finding a live moving louse with wet detection combing; nits alone may be empty or non-viable.
  • Check household members and treat those with live lice on the same day; routine treatment of uninfested contacts is unnecessary.
  • Use wet combing on days 1, 5, 9 and 13 with a check on day 17, or a licensed physical insecticide exactly as directed.
  • Many dimeticone products require a second application after seven days; resistance is less relevant to a physical coating mechanism.
  • Pubic lice warrants treatment of recent sexual contacts and an STI screen; eyelash involvement needs eye-safe specialist advice.
  • Body lice control depends on laundering or replacing infested clothing and bedding plus access to washing and social support.
  • Bite reactions are managed with source control, cold compresses, oral non-sedating antihistamine and appropriate topical anti-inflammatory care, not routine antibiotics.
  • Treat anaphylaxis with intramuscular adrenaline and assess expanding erythema, fever or necrosis separately from a large local allergic reaction.

Aetiology

01

Head-louse transmission

Pediculus humanus capitis spreads mainly through direct hair-to-hair contact; jumping, flying and dirty hair are myths.

02

Body and pubic lice

Body lice live chiefly in clothing seams, while pubic lice spread through close bodily contact and sometimes affect coarse hair or eyelashes.

03

Arthropod saliva

Mosquito, flea, bedbug and other bites inject salivary antigens that provoke immediate or delayed itchy hypersensitivity papules.

04

Exposure ecology

Pets, travel, accommodation, occupational contact, clothing and household clustering help locate the source without assigning blame.

Pathophysiology

  1. 1
    Blood feeding and eggs

    Lice feed repeatedly and cement nits to hair shafts or clothing fibres; empty shells can persist after eradication.

  2. 2
    Hypersensitivity itch

    Immune response to saliva and faeces produces pruritus, excoriation and sometimes delayed symptoms despite active infestation.

  3. 3
    Papular urticaria

    Recurrent arthropod bites trigger grouped itchy papules with central puncta and unusually prolonged lesions, particularly in susceptible children.

  4. 4
    Barrier injury

    Repeated scratching creates erosions, crust, persistent pigment change and an entry portal for staphylococcal or streptococcal infection.

Clinical features and red flags

Live head louse

A grey-brown moving insect found by detection comb confirms active head-lice infestation.

Nits without lice

Firm eggshells attached to hair can remain after cure and do not alone justify treatment.

Pubic or eyelash lice

Coarse-hair lice, blue-grey macules or nits on eyelashes require sexual-health or ophthalmic context.

Papular bite crops

Grouped itchy papules with a central punctum on exposed sites support arthropod hypersensitivity.

Anaphylaxis physiologyRed flag

Sudden airway swelling, wheeze, hypoxia, hypotension or collapse after a bite or sting requires intramuscular adrenaline.

Red flags requiring action

  • Airway, breathing or circulation compromise after a bite, expanding severe infection, fever with travel or tick exposure, eyelash lice with ocular injury, unexplained genital lice in a child or widespread infestation in a vulnerable person requires urgent assessment.

Investigations

  1. 01
    Wet detection combingFirst step
    Why
    Confirm active head lice before treatment.
    Interpretation and limitations
    A live louse is diagnostic; dandruff and empty nits are not.
  2. 02
    Exposure and household map
    Why
    Identify contacts and likely flea, bedbug, travel or animal sources.
    Interpretation and limitations
    Distribution and timing guide environmental action; one papule cannot identify an insect species reliably.
  3. 03
    Bacterial swab
    Why
    Assess pus or crust after scratching when infection is clinically present.
    Interpretation and limitations
    Do not swab intact allergic papules or prescribe antibiotics for itch alone.
  4. 04
    STI testing with consent
    Why
    Assess co-infection when pubic lice is diagnosed.
    Interpretation and limitations
    Offer site- and exposure-appropriate testing and partner notification without moral judgement.
  5. 05
    FBC and targeted vector testing
    Why
    Investigate anaemia or systemic febrile illness after heavy infestation or relevant travel.
    Interpretation and limitations
    Tests follow symptoms and epidemiology; routine blood panels are unnecessary for ordinary head lice.

Differential diagnosis

01

Scabies

Nocturnal itch, burrows in finger webs and genital nodules with close-contact spread favour mites over lice or exposed-site bites.

02

Eczema or folliculitis

Chronic confluent dermatitis or follicle-centred pustules lacks live lice and the characteristic clustered punctate exposure pattern.

03

Urticaria

Migrating raised wheals resolve individually within 24 hours without a punctum, unlike persistent excoriated insect-bite papules.

04

Delusions of infestation

A fixed infestation belief without objective insects requires respectful dermatological examination and avoidance of harmful repeated pesticide exposure.

Management

01Confirmed head liceTreat and recheckFirst stepA live louse is found by detection combing.+
  1. 1Check household members and treat all confirmed cases on the same day.
  2. 2Use scheduled wet combing or a licensed dimeticone product, repeating at seven days when its instructions require it.
  3. 3Recheck for live lice after the completed regimen and distinguish reinfestation, under-application and nits from failure.
02Pubic or body liceAddress context and contactsLice involve pubic or body sites or clothing seams.+
  1. 1For pubic lice, arrange treatment, recent partner management and STI screening; obtain specialist advice for eyelashes.
  2. 2For body lice, hot-launder or replace clothing and bedding and support access to washing facilities.
  3. 3Assess secondary infection, anaemia, vulnerability and safeguarding without stigmatising the patient.

Complications

01

Secondary infection

Excoriated scalp or bite lesions can subsequently develop bacterial impetigo, spreading cellulitis and tender regional lymphadenopathy.

02

Anaemia in heavy infestation

Severe chronic lice burden can contribute to iron deficiency, especially in vulnerable children or neglected adults.

03

Anaphylaxis

Some stings and bites trigger sudden life-threatening airway, respiratory or circulatory compromise requiring immediate intramuscular adrenaline treatment.

04

Psychological and social harm

Stigma, persistent sleep loss, unnecessary school exclusion and repeated pesticide overuse can exceed the infestation's direct physical burden.

Monitoring and follow-up

  • Recheck for live lice after the complete regimen rather than treating persistent nits.
  • Audit product quantity, coverage, contact time and repeat date before declaring resistance.
  • Review bite lesions for reduced itch and absence of new crops after source control.
  • Escalate breathing difficulty, hypotension, fever, spreading infection or tick-associated systemic symptoms.
  • Document STI, safeguarding and social-support actions sensitively for pubic or body lice.

Special situations

Live lice define activity

Adherent empty eggs can remain for months and are not proof that treatment failed.

Lice do not jump

Head-to-head contact, not airborne spread or unclean hair, drives most transmission.

Product timing differs

Dimeticone formulations have different contact times, making package-specific instruction essential.

Bite pattern guides source

Crops on exposed sites and household or pet clustering are more informative than lesion colour alone.

Common pitfalls

  1. 01

    Diagnosing head lice from nits alone and repeatedly treating a cleared scalp.

  2. 02

    Using too little lotion to cover thick or long hair.

  3. 03

    Treating every household member prophylactically without checking for live lice.

  4. 04

    Giving antibiotics for sterile bite hypersensitivity without infection.

  5. 05

    Missing STI or safeguarding assessment when pubic lice occurs in a concerning context.

Practice

Two practice questions

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Question 1 of 2
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DermatologyOriginal SBA

Nits after school screening

A child has several old nits attached to hair but careful wet detection combing finds no live lice. What is the best interpretation?

Choose one answer, then submit
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Sources and review status3 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NHS head lice and nitsLive-louse diagnosis, wet combing and treatment options.
  • British Association of Dermatologists head liceTransmission, treatments, contacts and failure assessment.
  • NHS insect bites and stingsBite care, infection and anaphylaxis warning symptoms.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
03Insect-bite reactionControl source and inflammationGrouped itchy papules fit bites without anaphylaxis or invasive infection.+
  1. 1Identify and remove the likely environmental source, including pet or professional pest assessment when indicated.
  2. 2Use cold compresses, a non-sedating antihistamine and brief site-appropriate topical corticosteroid for itch.
  3. 3Safety-net systemic allergy, fever, spreading pain, target-like rash after tick exposure and persistent unexplained lesions.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
A physical head-lice treatment that coats lice and has no conventional neurotoxic resistance mechanism.

Dimeticone 4% lotion

Apply to dry hair and scalp until fully covered, leave for the product-specified period and repeat after seven days when directed.

Follow the exact licensed product because contact times differ, avoid flames and heat while hair is treated, protect eyes and do not use incomplete leftover quantities.

A generally non-sedating option for symptomatic itch and wheal reduction.

Cetirizine 10 mg tablets

Adults and people aged 12 years or older take 10 mg orally once daily when bite-related itch warrants an antihistamine.

Somnolence can occur; consider driving, alcohol and renal adjustment, and do not substitute it for adrenaline in anaphylaxis.