Scabies

Scabies is an intensely itchy skin infestation caused by Sarcoptes scabiei var. hominis, a microscopic, obligate human ectoparasite mite that burrows into the outermost layer of the skin (the stratum corneum) to live and lay eggs.^[1][2] It is common and highly contagious, and the World Health Organization designated it a Neglected Tropical Disease in 2017 given its global burden: an estimated 200 million people are affected at any given time worldwide, with roughly 400 million new cases annually, and in some resource-poor settings 5-50% of children are affected.^[3] This chapter covers classical scabies — the far more common presentation, driven by direct, prolonged skin-to-skin contact and defined by its hallmark nocturnal itch — and crusted (Norwegian) scabies, a rare but far more contagious variant seen in immunocompromised, elderly, or physically or cognitively impaired patients that carries a dramatically higher mite burden, can spread by fomites as well as by direct contact, and requires more aggressive combination therapy.

Two facts should anchor every pharmacist encounter. First, scabies is not a marker of poor hygiene — anyone, in any household, can acquire it through the kind of close, sustained contact that happens every day between family members, intimate partners, and caregivers.^[4][5] Second, the single biggest determinant of whether a course of treatment actually works is not which scabicide is chosen but whether it is applied correctly to the entire relevant body surface, whether the scheduled second application happens on time, and — critically — whether every household member and close contact is treated simultaneously, regardless of whether each one has symptoms yet. A pharmacist who leads with these three points measurably improves the odds that a family's first treatment attempt actually succeeds.

Life cycle — why symptoms take weeks to appear

After mating on the skin surface, the female mite burrows into the stratum corneum, laying 2-4 eggs daily and depositing faecal pellets ("scybala") along the burrow as she goes.^[1] Eggs hatch into six-legged larvae within 2-4 days; the larvae create their own short burrows and wander on the skin for roughly 2 weeks before moulting through nymphal stages into adults, so the full mite life cycle runs approximately 2-3 weeks, and an adult female survives on the host for 1-2 months.^[1][2] Off the host, survival is short but genuinely variable by source: the European IUSTI guideline states adult mites die within 24-36 hours away from human skin, StatPearls describes immature stages persisting up to about 9 days at typical room temperature (15-25°C), and the Canadian Paediatric Society's own patient-facing figure states mites can "live off skin for up to 3 days" — the practical counselling point is the same regardless of the exact number: environmental measures need to cover recently used items, not the whole home indefinitely (see Non-Pharmacologic Treatment).^[2][1][4]

Symptoms are a hypersensitivity reaction, not a direct mite effect — which is why timing varies so much

The intense itch that defines scabies is not caused directly by the mite's burrowing but by a delayed (type IV) hypersensitivity reaction to the mite itself and its faecal and egg products.^[2] With a first-ever infestation, sensitization takes time to develop — cited windows range from about 3-6 weeks (IUSTI) to 4-10 weeks (StatPearls) — so a newly infested person can be genuinely asymptomatic, and unknowingly contagious, for a month or more.^[2][1] With re-infestation, a person already sensitized from a prior episode develops symptoms much faster, within hours to a few days.^[2][1] This asymptomatic-but-contagious window is exactly why household and close-contact treatment cannot wait for every contact to develop symptoms of their own (see Choose Initial Treatment).

Classic distribution — different in adults than in infants and young children

In older children and adults, itch is characteristically worse at night, and burrows and papules cluster in the finger and toe web spaces, the flexor aspects of the wrists, elbows, and axillae, the periumbilical area and waistline, the buttocks, and the genitalia (the penis and scrotum in men, the areola and breasts in women); the head, palms, and soles are usually spared in adults.^[2][5] Infants and young children are different: the Canadian Paediatric Society's own patient handout notes the rash can additionally appear on "the head, face, neck, chest, abdomen, and back", and Alberta's provincial patient-education material similarly notes the scalp, face, palms, and feet may be involved — sites essentially never affected in an infested adult.^[4][5] Recognizing this different distribution matters clinically, since a facial or scalp rash in an itchy infant is easy to attribute to eczema or a viral rash rather than scabies.

The burrow — the one genuinely pathognomonic finding, and why it is so often missed

The burrow is a thin, wavy, grey-to-brown line roughly 0.5-1 cm long, sometimes with a tiny vesicle or fleck of debris at the end marking where the female mite currently sits — the single pathognomonic physical finding of scabies.^[2][1] In practice it is rarely seen clearly, since scratching, secondary eczematization, and secondary bacterial infection obscure it in most real-world presentations.^[2] What is usually seen instead is a scattering of small, excoriated, erythematous papules, sometimes topped with haemorrhagic crusts, along with less specific findings such as vesicles (usually where a burrow begins) and firm, itchy nodules, discussed below.^[2]

A scabies burrow — the thin, wavy line is the mite's tunnel through the outer skin layer; the surrounding scaly patch reflects scratching. (Photo: Michael Geary, public domain, via Wikimedia Commons)

Nodular scabies

A minority of patients develop firm, intensely itchy, reddish-brown nodules, typically in moist, thin-skinned areas such as the axillae, groin, and genitalia — a hypersensitivity reaction to mite antigens rather than a site of active infestation.^[1] These nodules matter for a reason explored further in Monitoring & Follow-Up: they can persist for weeks to months after mites have been fully eradicated and do not, by themselves, indicate treatment failure or ongoing infestation.

Crusted (Norwegian) scabies — a distinct, far more contagious entity

The term "Norwegian scabies" is now discouraged in favour of "crusted scabies", though the two names refer to the same condition.^[2] Crusted scabies develops when a host's immune or physical ability to control mite proliferation through scratching is impaired: it is seen in patients with severe immunodeficiency (advanced HIV/AIDS, HTLV-1 infection, malignancy), those on immunosuppressant drugs or biologic therapy, patients with neurological disease causing reduced sensation or reduced ability to scratch, immobile or bedridden patients, and some genetically susceptible individuals; it is also disproportionately seen in older adults and residents of long-term care.^[2][1] Instead of the roughly 10-15 mites carried by a person with classical scabies, a patient with crusted scabies can harbour thousands to millions of mites.^[2][1][3] Counterintuitively, pruritus is often mild or entirely absent — a genuine diagnostic trap, since the itch that normally prompts a scabies work-up may simply not be there.^[2] Instead, the skin shows generalized, poorly defined, erythematous, fissured plaques covered by thick scale and crust, often with a yellow-to-brown, warty (verrucous) texture concentrated over bony prominences such as the finger joints, elbows, and iliac crest; malodorous, secondarily infected lesions are common.^[2] Because the presentation looks so much like psoriasis, chronic eczema, or seborrheic dermatitis, crusted scabies is a well-documented diagnostic pitfall.^[1] The clinically vital point, explored further below, is that this enormous mite burden and heavy skin-scale shedding make crusted scabies transmissible by fomites — bedding, clothing, furniture, even a shared wheelchair or hospital gurney — in a way classical scabies essentially never is, which is why a suspected or confirmed case triggers a very different, more urgent response (see Red Flags & Refer and Non-Pharmacologic Treatment).^[1][2]

• Any household member, intimate partner, or regular caregiver of a person with active scabies — the dominant risk factor, since transmission requires prolonged, direct skin-to-skin contact of the kind that happens routinely within these relationships.^[5][2]
• Sexual contact — scabies can be, and often is, sexually transmitted, which shapes both partner-notification practice and the STI-screening recommendation discussed in Assessment & Diagnosis.^[2]
• Crowded or congregate living: households with several members sharing sleeping space, long-term care and nursing home residents, correctional facilities, shelters, and populations affected by mass displacement all see disproportionate scabies transmission and are the settings where population-level mass-treatment programs are used (see Non-Pharmacologic Treatment).^[2]
• Children and their direct caregivers, simply because of the volume of close physical contact involved in routine care.^[4]
• For crusted scabies specifically (a distinct risk profile from classical scabies): significant immunosuppression (advanced HIV/AIDS, HTLV-1, malignancy, immunosuppressant or biologic drug therapy), neurological disease causing reduced sensation or reduced ability to scratch, immobility, cognitive impairment, and older age, especially in a long-term care setting.^[2][1]
• Lower-resource settings globally carry a disproportionate burden — the World Health Organization cites 5-50% prevalence among children in some resource-poor areas — but scabies occurs across every socioeconomic group in Canada, and an individual case is never a reflection of a family's hygiene or living standards.^[3][4][5]

History and examination

Ask specifically about the timing and character of the itch (nocturnal predominance is a strong clue), the distribution of lesions, and — critically — whether anyone else in the household, or a sexual partner, has similar symptoms; a positive contact history is itself one of the most useful diagnostic clues available.^[2][5]

The 2020 IACS consensus criteria

The International Alliance for the Control of Scabies (IACS) published consensus diagnostic criteria in 2020, developed through a formal Delphi process among international experts, organizing scabies diagnosis into three tiers of certainty: confirmed scabies (level A), which requires direct visualization of a mite, egg, or faecal pellets by microscopy or dermoscopy; and clinical scabies (level B) and suspected scabies (level C), both based on the pattern of clinical signs, symptoms, and history rather than direct visualization. The IACS criteria are explicitly not intended for atypical presentations, including crusted scabies, bullous scabies, scabies in immunocompromised patients, or scabies in elderly, cognitively impaired, or bedridden patients — these variants are diagnosed on clinical grounds and with a lower threshold of suspicion, given the consequences of a missed diagnosis.

Dermoscopy

Handheld dermoscopy at roughly ×10 magnification can identify burrows and, at the end of an intact burrow, the mite's anterior body segment as a small triangular structure often described as resembling a jetliner's contrail or the silhouette of a delta-wing jet (the "delta-wing jet sign") — a fast, non-invasive way to support the diagnosis at the point of care, though it is less reliable on darkly pigmented or very hairy skin.^[1]

Skin scraping and microscopy

A skin scraping — classically taken from an intact burrow, sometimes aided by a drop of mineral or immersion oil to bring the mite to the surface — examined under low-power microscopy for a mite, egg, or faecal pellets ("scybala") remains the traditional confirmatory test.^[2][1] It is genuinely insensitive in practice: sampling error is common, the technique is time-consuming, and — importantly for counselling a patient or a referring colleague — a negative scraping does not exclude scabies, particularly when only a few burrows are present.^[2][1]

Sarcoptes scabiei viewed under an optical microscope (×20) — the actual finding a skin scraping is designed to catch. (Photo: Arthur Goldstein, CC BY-SA 4.0, via Wikimedia Commons)

STI screening in sexually active patients

Because scabies can be sexually transmitted, the European IUSTI guideline recommends offering screening for other sexually transmitted infections, including HIV, to a sexually active patient diagnosed with scabies (grade A recommendation) — a genuinely easy point to overlook when the presenting complaint is simply an itchy rash.^[2]

Differential diagnosis

• Confirm the diagnosis where practical — by history, characteristic distribution, burrow visualization, dermoscopy, or skin scraping — while recognizing that a negative scraping does not exclude the diagnosis.
• Distinguish classical from crusted scabies early, since the two require substantially different treatment intensity and urgency.
• Eradicate mites with a correctly applied scabicide covering the entire relevant body surface, and plan the scheduled second application from the outset rather than as an afterthought.
• Treat every household member and close/sexual contact simultaneously, regardless of whether they have symptoms yet, given the weeks-long asymptomatic-but-contagious window.
• Scope environmental decontamination appropriately — genuinely important but targeted for classical scabies, more extensive for crusted scabies given its fomite-driven contagiousness.
• Relieve pruritus and treat any secondary bacterial infection.
• Set accurate expectations for the post-treatment itch timeline so it is not mistaken for treatment failure.
• Recognize true treatment failure or reinfestation versus the far more common causes of apparent failure, and escalate appropriately, including institutional/public-health notification when relevant.

Permethrin 5% cream — first line, and application technique is everything

Permethrin is a synthetic pyrethroid that disrupts sodium-channel function in the mite's nervous system, causing paralysis and death; the platform's own Permethrin monograph confirms the 5% w/w cream formulation is specifically indicated for scabies, distinct from the 1% crème rinse used for head lice. Correct technique matters more for this drug than for perhaps any other topical antiparasitic in this platform's drug tables: apply to every area of the body from the neck down to the soles of the feet — not just the visibly affected areas — including the web spaces of the fingers and toes, under the free edge of the fingernails and toenails (a soft brush can help), the groin and genitalia, and the umbilicus; in infants, older adults, and immunocompromised patients, extend the application to the scalp, face (avoiding the eyes and mouth), neck, and ears as well, since these sites are not reliably spared in these groups (see Recognize the Condition and Special Populations).^[2][1] Leave in place for 8-14 hours (a full overnight application is the simplest way to achieve this), then wash off; the skin should be cool and dry before application, and clean clothing and bedding should follow.^[2] A second application 7-14 days later is not optional — permethrin has limited ovicidal activity, so any egg present at the time of the first application can still hatch afterward, and the second application is timed to kill newly hatched larvae before they mature and restart the cycle. Permethrin 5% cream is licensed from 2 months of age and is considered safe in pregnancy and lactation.^[2]

Oral ivermectin — the main alternative, with real, guideline-acknowledged uncertainty in the comparative evidence

Prescriber-directed Oral ivermectin 200 mcg/kg is given as a single dose and, per essentially every current guideline, repeated — the exact interval is genuinely guideline-dependent: the European IUSTI guideline specifies 7 days, while the CDC's 2021 STI treatment guidelines specify 14 days; follow the specific prescriber's chosen protocol rather than assuming one interval is universal.^[2][6] Ivermectin is considered scabistatic rather than fully scabicidal — like permethrin, it has limited ovicidal activity, which is exactly why the second dose exists: to kill mites hatching from eggs that survived the first dose.^[1] Taking the dose with food meaningfully increases oral bioavailability and is now the practical recommendation specifically for scabies dosing, even though ivermectin's general product labelling elsewhere directs an empty stomach.^[6] A 2019 CADTH (Canadian Agency for Drugs and Technologies in Health) Rapid Response review of the comparative evidence found no conclusive difference in cure rates between oral and topical ivermectin, but noted topical ivermectin may carry a lower rate of persistent post-treatment itching; the same review found oral ivermectin may be less effective than permethrin cream at 1-2 weeks after treatment, though the difference disappeared at later follow-up — and, in a transparency point worth passing on to a patient choosing between options, the reviewers noted that most of the underlying clinical trials came from Asia, the UK, Europe, and Japan, with limited data generated in, or necessarily generalizable to, a Canadian population.^[7] Oral ivermectin should be avoided in pregnancy and in a patient weighing less than 15 kg.^[2]

A platform-specific note on ivermectin some international literature and the CDC's own STI treatment guidelines describe a topical ivermectin 1% cream, applied with the same neck-down technique as permethrin, as an additional alternative for classical scabies.^[6] This platform's only ivermectin monograph (brand ROSIVER, ivermectin 1% cream) is the same strength and vehicle studied in that literature, but it is Health Canada-labelled specifically for rosacea, not scabies, so this chapter does not link oral or topical ivermectin to that monograph — both are presented as plain text pending a genuinely antiparasitic-labelled ivermectin product being added to this platform's Drug Database.

Alternative agents with limited or no current Canadian availability

International guidelines, particularly the European IUSTI guideline, also list benzyl benzoate lotion 10-25% (applied nightly on 2 consecutive days, re-applied at 7 days) as a recommended first-tier option, and malathion 0.5% aqueous lotion, sulphur 6-33% cream/ointment/lotion (applied on 3 successive days), and synergized pyrethrins foam as alternative options.^[2] A direct query of the Health Canada Drug Product Database performed while authoring this chapter found no currently marketed human benzyl benzoate product in Canada (the only historical entry was a veterinary product, cancelled in 2002) and no malathion product registered under that active-ingredient name at all — these are not practical Canadian options today, whatever their standing in other jurisdictions' guidelines.^[8] Crotamiton (Eurax) 10% cream does retain a Health Canada Drug Identification Number, but the same database query found its status listed as Dormant (as of a June 2023 status update) — meaning it has not actually been sold in Canada over the preceding period despite not being formally cancelled, so a Canadian pharmacist should not assume practical availability.^[8] Lindane is a special case worth being explicit about: it is no longer recommended by current guidelines because of documented neurotoxicity risk (including seizures, particularly with over-application, use on broken skin, or use in young children or people under 50 kg), and a direct query of the Health Canada Drug Product Database confirms that every lindane product ever registered in Canada — nine separate brands across five decades — is now listed as Cancelled Post Market, the last as of August 2004.^[2][8] None of these five agents (benzyl benzoate, malathion, sulphur, crotamiton, lindane) are included as active recommendations in this chapter's drug table; they are presented for awareness only, since a patient's own research — particularly anything sourced from American or European material — may reference them.

Crusted (Norwegian) scabies — combination therapy is mandatory, not a stronger version of the same regimen

Because a patient with crusted scabies can carry a mite burden orders of magnitude higher than in classical scabies, single-agent dosing at the standard interval is inadequate, and treatment failure with a single-dose topical scabicide or a single course of oral ivermectin is well documented.^[6] Current guidance directs a topical scabicide combined with oral ivermectin, both intensified well beyond standard classical-scabies dosing: permethrin 5% cream (or, where available, benzyl benzoate 25% lotion) applied daily for 7 days, then twice weekly until cure is confirmed, together with oral ivermectin 200 mcg/kg on days 1, 2, and 8; for more severe cases — guided by persistent live mites on a follow-up skin scraping — additional ivermectin doses are added on days 9 and 15, and in the most severe cases on days 22 and 29 as well.^[2][6] There is no firm consensus on the optimal frequency of the topical component in the most severe cases, and management of confirmed or strongly suspected crusted scabies should involve a dermatologist or infectious-diseases specialist rather than being run as a purely pharmacist-initiated plan — this is one of the clearest "refer" situations in this entire chapter (see Red Flags & Refer).

Household, close-contact, and sexual-partner treatment is not optional

Because an infested person can be contagious for weeks before developing symptoms, and because scabies spreads so efficiently through the sustained skin contact that defines a household, every household member and close physical/sexual contact should be treated simultaneously with the diagnosed patient, on the same schedule, regardless of whether each individual has symptoms of their own.^[4][9] Sexual partners specifically should be advised of the diagnosis and offered treatment; the European IUSTI guideline recommends a partner look-back period of 2 months and advises against sexual contact until the patient and all partners have completed treatment.^[2]

Symptomatic relief

Itch, particularly nocturnal a non-sedating oral antihistamine (cetirizine) for daytime use, or a sedating option (diphenhydramine, or hydroxyzine for more severe itch) at bedtime. Local irritation or post-treatment dermatitis a short course of a low-potency topical corticosteroid (hydrocortisone) and regular emollient use — the European guideline specifically endorses repeated application of emollients plus oral antihistamines and mild topical corticosteroids for post-treatment itch once active infestation has actually been treated (see Monitoring & Follow-Up for why timing this correctly matters).^[2] Secondary bacterial infection treat per the usual localized (topical mupirocin) or spreading (oral cephalexin, or clindamycin/sulfamethoxazole-trimethoprim where penicillin allergy or MRSA is a specific concern) skin and soft tissue infection pathway.

Environmental measures — scoped differently for classical versus crusted scabies

Because classical scabies spreads overwhelmingly through direct skin contact rather than fomites, environmental decontamination should be targeted, not exhaustive: machine wash clothing, bedding, and towels used in the few days before treatment in hot water (a wash cycle of at least 50°C) and dry on a hot cycle; dry-clean items that cannot be washed; and seal anything that can be neither washed nor dry-cleaned in an airtight plastic bag for at least 72 hours, though international guidance favours a full week as a more conservative safety margin given the range of off-host survival estimates discussed in Recognize the Condition.^[9][2] Vacuum mattresses, upholstered furniture, and carpets in rooms used by the infested person, particularly on the first day of treatment.^[9] For crusted scabies specifically, extend these measures further and treat them as genuinely necessary rather than optional: the enormous mite burden and heavy skin-scale shedding in this variant make fomite transmission a real risk in a way it essentially is not for classical scabies, so bedding, clothing, and shared equipment (wheelchairs, commodes, hospital linens) need more rigorous, facility-level attention, often coordinated with infection control in an institutional setting.^[1][2]

Household and contact measures

• Treat every household member and close/sexual contact at the same time as the diagnosed patient — covered in Choose Initial Treatment, but worth repeating as the single highest-yield non-pharmacologic step available.^[4][9]
• Avoid skin-to-skin contact and avoid sharing clothing, towels, and bedding until the patient and their close contacts have completed treatment.^[9]
• A child or adult may return to daycare, school, or work once the first treatment application has actually been completed — prolonged exclusion beyond that point is not necessary or evidence-based.^[4]

Written information for patients

The European IUSTI guideline specifically recommends giving every suspected or confirmed case clear written information about the diagnosis, transmission, and treatment plan — a genuinely simple step that improves adherence to the household-treatment and environmental measures above, which depend on the whole family understanding and following through on a somewhat involved plan.^[2]

Pregnancy

Breastfeeding

Permethrin is considered compatible with breastfeeding given minimal systemic absorption from topical use.^[2] Confirm current specifics against the drug's own Drug Database entry and product monograph before recommending.

Pediatrics

Permethrin 5% cream is licensed from 2 months of age.^[2] In infants and young children, remember the different lesion distribution described in Recognize the Condition (scalp, face, neck, palms, and soles can be involved, unlike in an older child or adult) and extend the application technique to cover the scalp and face (avoiding the eyes and mouth) accordingly.^[4][5] Oral ivermectin should be avoided in a child weighing less than 15 kg regardless of age.^[2]

Older adults, immunocompromised patients, and long-term care

These are exactly the populations at disproportionate risk for crusted scabies (see Recognize the Condition and Risk Factors), and pruritus may be mild or absent even with a very high mite burden — a reason to keep a lower threshold of suspicion for a new or worsening scaly eruption in this population rather than waiting for the classic itch to appear.^[2][1] A confirmed or strongly suspected case in a long-term care or institutional setting should trigger facility-level infection-control involvement, not only individual patient treatment (see Red Flags & Refer).

Renal and hepatic impairment

No specific dose adjustment is described for topical permethrin given its minimal systemic absorption. For oral ivermectin, involve the prescriber for dosing in significant hepatic impairment; standard weight-based dosing is otherwise used.

• Confirm the patient — and every household/close contact being treated — understands, and has scheduled, the second application before the encounter ends; this single point is one of the most common reasons an otherwise appropriate treatment appears to "fail."
• Set expectations for post-treatment itch explicitly, before it happens: the European IUSTI guideline defines successful clearance as no active lesions and no nocturnal pruritus 1 week after the end of treatment, but also states plainly that post-treatment itch may persist for up to 2-4 weeks even after mites have been fully eradicated — a figure echoed by Alberta's own provincial patient-education material.^[2][9] This single counselling point is likely the highest-yield thing a pharmacist can say at the end of a scabies encounter, since unrecognized post-treatment itch is a well-documented driver of unnecessary retreatment.
• Where a follow-up skin scraping is available, the IUSTI guideline recommends a follow-up visit 2 weeks after completing treatment for a formal test-of-cure examination, particularly useful when there is genuine diagnostic or treatment-failure uncertainty.^[2]
• At any follow-up contact, confirm that every household member and close/sexual contact was actually treated on schedule, since an untreated contact is the most common source of apparent reinfestation.
• For crusted scabies specifically, follow-up skin scrapings guide whether additional ivermectin doses (days 9, 15, and, for severe cases, 22 and 29) are actually needed — this should be managed by the treating specialist rather than the community pharmacist alone.^[6][2]

1. Reassess whether this is actually persistent infestation or expected post-treatment itch. Itch alone, with no new burrows, papules, or nodules, in the first 2-4 weeks after a correctly completed treatment course is expected and is not, by itself, evidence of treatment failure (see Monitoring & Follow-Up).^[2][9]
2. Confirm technique and adherence before assuming the agent failed. Was the cream genuinely applied to the entire body surface — including web spaces, under the nails, and (in an infant or immunocompromised patient) the scalp and face — rather than just the visibly affected areas? Was the full 8-14 hour contact time observed? Was the scheduled second application actually completed on time?
3. Rule out reinfestation from an untreated contact. A household member, intimate partner, or other close contact who was missed, declined treatment, or was not treated on the same schedule is a common and easily overlooked source of apparent treatment failure.^[4][9]
4. Reconsider crusted scabies if the presentation is unusually extensive, scaly, or crusted, or is occurring in an immunocompromised, elderly, or institutionalized patient — standard classical-scabies dosing is genuinely inadequate for this variant, and persistent live mites on a follow-up scraping after standard therapy should trigger the combination regimen, not simply a repeat of the same single-agent course (see Choose Initial Treatment).^[6]
5. True treatment failure — persistent, confirmed active infestation despite adherence, correct technique, and genuine household/contact treatment — warrants prescriber involvement to reconsider agent (switching between permethrin and oral ivermectin, or vice versa) rather than simply repeating the same regimen a third time.
6. Persistent localized nodules (see Nodular Scabies in Recognize the Condition) with no new burrows or spreading rash reflect a lingering hypersensitivity reaction, not ongoing infestation, and can persist for weeks to months — manage symptomatically rather than retreating for scabies again.^[1]

• Applying a scabicide only to visibly affected skin rather than the entire body surface from the neck down (or the entire body, including the scalp and face, in an infant or immunocompromised patient) — this is the single most common technique error and a major driver of apparent treatment failure.^[2][1]
• Skipping or mistiming the scheduled second application, whether for permethrin or oral ivermectin — neither agent reliably kills eggs, and the second dose exists specifically to catch newly hatched mites.^[1]
• Treating only the symptomatic individual and not the rest of the household and close/sexual contacts — the single most common reason a family experiences prompt reinfestation after an apparently successful individual treatment.^[4][9]
• Retreating repeatedly for persistent itch alone in the first 2-4 weeks after a correctly completed course, without checking for new lesions first — this is expected post-treatment itch, not treatment failure, and unnecessary retreatment carries its own irritant burden.^[2]
• Missing crusted scabies because the patient is not itchy — pruritus can be mild or absent in this variant even with a massive mite burden, and the diagnosis is easily mistaken for psoriasis or eczema.^[2][1]
• Treating a suspected crusted scabies case with standard single-agent, single-course classical-scabies dosing rather than the intensified combination regimen it requires.^[6]
• Assuming an itchy rash is "just eczema" or a nonspecific dermatitis and reflexively recommending a topical corticosteroid alone, without considering scabies in the differential — prolonged, unsupervised corticosteroid use on an unrecognized infestation ("scabies incognito") can blunt the classic presentation, delay diagnosis, and in an already-immunosuppressed patient may contribute to progression toward crusted scabies.^[2][1]
• Assuming benzyl benzoate, malathion, sulphur, crotamiton, or lindane are readily available Canadian options on the strength of American or European literature — a direct Health Canada Drug Product Database check performed for this chapter found none of them practically available in Canada today (see Choose Initial Treatment).^[8]
• Overlooking the STI-screening conversation in a sexually active patient with confirmed scabies.^[2]
• Using stigmatizing or hygiene-blaming language when discussing the diagnosis, rather than leading with the fact that scabies spreads through the kind of close contact that happens in any household, regardless of cleanliness.^[4][5]

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Scabicidal / Antiparasitic Therapy

Neither agent reliably kills eggs — a correctly timed 2nd dose is expected for every patient, not a sign that the first dose failed. Treat the entire household and close/sexual contacts on the same schedule.

Alternative Agents Referenced in Non-Canadian Literature — Awareness Only

None of the five agents below are practical Canadian options today. Each status was confirmed by a direct query of the Health Canada Drug Product Database while authoring this chapter, not assumed from prior editions or non-Canadian sources.

Symptomatic Relief

For pruritus and post-treatment irritation while the antiparasitic course does the actual work of clearing the infestation. Itch commonly persists 2-4 weeks after fully successful treatment and is not itself a reason to retreat.

Secondary Bacterial Infection of Excoriated Skin

Reserve for genuine impetiginization or cellulitis arising from scratching-related skin breakdown; escalate to systemic therapy if infection is spreading. Untreated superinfection carries a rare but real risk of complications including post-streptococcal glomerulonephritis.