Lesson
Localize the Arthropod Before Treating It
Head lice, body lice, pubic lice, and scabies occupy different habitats. Pruritus reflects hypersensitivity and can lag infestation or persist after organisms are gone.
- Louse versus mite
- Habitat
- Life cycle
- Hypersensitivity
- Secondary infection
Live louse and near-scalp nits
Seams carry organisms and eggs
Sexual-health contact pathway
Burrow, papule, and contact network
Map habitat to disease
Head lice cling to scalp hair. Body lice mainly live in clothing seams. Pubic lice attach to coarse hair. Sarcoptes scabiei mites burrow in the stratum corneum. Pets do not transmit human head lice.
Separate symptoms from viability
First-exposure itch can take weeks to develop, while post-treatment itch can persist. Live lice, new burrows, new papules, and objective mites or eggs answer activity more reliably than itch alone.
Use life cycle to time therapy
Egg killing differs by drug. Products that do not reliably kill eggs need a repeat timed after hatching and before mature organisms reproduce. Scabies treatment also coordinates a second exposure when required.
Protect injured skin
Excoriation can cause impetigo or cellulitis. Spreading redness, warmth, pain, pus, fever, lymphangitis, or systemic illness requires evaluation beyond antiparasitic treatment.
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Lesson
Confirm Active Head Lice Without Stigma
Head lice are best diagnosed by a live crawling louse. Nits close to the scalp support recent infestation, but dandruff and distant empty casings are commonly misidentified.
- Live louse
- Nit proximity
- Fine comb
- Nape and ears
- No hygiene blame
Bright light and fine comb
Best evidence of active infestation
Near-scalp attachment supports viability
Direct hair contact drives spread
Find live organisms
Use bright light, section the hair, and comb from scalp outward. Concentrate behind the ears and at the nape. Nymphs and adults move quickly and avoid light.
Interpret nits accurately
Nits are firmly attached. Those within one quarter inch of the scalp may be viable. Distant nits are usually hatched, dead, or empty and do not by themselves prove active infestation.
Reject false biology
Head lice crawl. They do not jump or fly. Direct hair-to-hair contact is the main transmission route, while pets do not acquire or spread human head lice.
Remove stigma
Head lice are not evidence of poor hygiene and do not transmit disease. Use neutral language and protect privacy while organizing examination, treatment, and return to school.
Quick check
Lesson
Choose a Head-Lice Product by Biology and Label
Permethrin, pyrethrins, ivermectin, spinosad, and malathion differ in age, egg activity, resistance, retreatment, formulation, and safety.
- Permethrin 1 percent
- Pyrethrins
- Ivermectin 0.5 percent
- Spinosad 0.9 percent
- Malathion 0.5 percent
Repeat needed when eggs survive
Usually one dry-hair application
Repeat only for live lice on day seven
No flame or electrical heat while wet
Use pyrethroids precisely
Permethrin 1 percent is approved from age two months and may need day-nine retreatment. Pyrethrins with piperonyl butoxide begin at age two years, need repeat treatment, and require chrysanthemum or ragweed allergy review.
Place current ivermectin accurately
Ivermectin lotion 0.5 percent is now OTC from age six months. It is usually a single dry-hair application and should not be repeated without clinician advice. Do not confuse it with off-label oral ivermectin.
Use spinosad by live-louse findings
Spinosad 0.9 percent is labeled from age six months and kills lice and unhatched eggs. Repeat only if live crawling lice are seen seven days after the first treatment. Nit combing is optional for the label regimen.
Keep malathion fire safety visible
Malathion 0.5 percent begins at age six years and is flammable while hair is wet. Avoid smoking, flames, hair dryers, curling devices, and straightening irons until the hair is dry.
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Lesson
Deliver the Full Scalp Dose and Time the Repeat
Correct active ingredient cannot overcome conditioner interference, incomplete saturation, wrong contact time, unsafe rinsing, or a retreatment schedule copied from another product.
- Dry versus prepared hair
- Full saturation
- Contact time
- Sink rinse
- Failure audit
Follow dry or prepared hair label
Volume follows length and density
Do not copy another product
Audit before reapplying
Prepare exactly as labeled
Do not use conditioner or combination shampoo and conditioner before a lice medicine. Confirm whether hair must be dry, how much product is needed, and whether a second bottle is required for long or dense hair.
Cover and time accurately
Saturate the scalp and all hair, protect eyes, use the exact leave-on interval, and wash hands. Rinse over a sink with warm rather than hot water when appropriate to limit skin exposure.
Comb with a purpose
Fine-toothed combing can remove lice and nits and support surveillance. It is helpful but not a universal proof of cure, and spinosad does not require nit removal for efficacy.
Audit failure before adding exposure
At eight to twelve hours, slowly moving lice may still be dying. If no dead lice are found or lice remain as active as before, consult before retreating. Review diagnosis, application, conditioner, contacts, reinfestation, and resistance.
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Lesson
Control Contacts and Environment Without Overreaction
Close contacts drive lice transmission. Focused examination, synchronized treatment, limited recent-item cleaning, and school inclusion replace prophylactic pesticide, fumigation, and no-nit policies.
- Contact examination
- Bed sharing
- Two-day item window
- No fumigation
- School inclusion
Coordinate treatment when indicated
Hot laundry and comb soaking
Off-host risk is low
Reject no-nit exclusion
Treat the contact network
Check household members and close contacts. Treat active infestations and people sharing a bed at the same time as directed. Do not apply insecticide prophylactically to every contact without evidence.
Clean what matters
Wash and high-heat dry clothing and bedding used during the two days before treatment. Soak combs and brushes in hot water, vacuum relevant surfaces, and seal nonwashable recent items when needed.
Stop excessive decontamination
Head lice survive poorly off the host. Spending extensive time and money cleaning the home is unnecessary. Fumigant sprays and fogs add inhalation and skin toxicity and should not be used.
Keep children in school
A child need not be sent home early. After treatment begins at home, the child can return. CDC, AAP, and school nurses oppose no-nit exclusion because distant or dead nits do not transmit like live lice.
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Lesson
Distinguish Pubic and Body Lice Pathways
Pubic lice require a sexual-health pathway, while body lice primarily require clean clothing, bathing, laundry access, and attention to vulnerable living conditions.
- Pubic lice
- Partner management
- STI evaluation
- Body lice
- Clothing seams
Treat all linked exposure
Keep insecticides away from eyes
Inspect clothes and bedding
Make the primary treatment possible
Treat pubic lice as sexual health
Apply the correct product to the prescribed coarse-hair sites, inform recent sex partners, avoid sexual contact until all are treated and infestation is excluded, and evaluate for other sexually transmitted infections.
Protect the eyes
Lice on eyebrows or eyelashes require clinician-directed removal or ophthalmic-grade therapy. Ordinary scalp or pubic lice products should not be placed near the eyes.
Find body lice in clothing
Body lice and eggs are usually found in seams rather than living continuously on skin. Inspect clothes and bedding when pruritus occurs in crowded or resource-limited settings.
Treat access as clinical
Regular bathing, clean clothing changes, hot laundering, bedding management, and housing support are primary body-lice interventions. Pediculicide is usually secondary when hygiene and laundering can be maintained.
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Lesson
Recognize Scabies and Its Contact Window
Classic scabies combines nocturnal pruritus, papules, and burrows in characteristic sites. Young children, older adults, immune compromise, and prior corticosteroids can change the pattern.
- Burrows
- Nocturnal itch
- Characteristic sites
- Dermoscopy
- Two-month contact history
Distribution supports diagnosis
Age changes morphology
Find mite, egg, or scybala
Asymptomatic contacts can transmit
Read distribution and history
Inspect finger webs, wrists, elbows, axillae, waist, buttocks, nipples, genitals, and other involved sites. In infants and young children, include head, neck, palms, and soles as directed.
Confirm when the question needs it
Dermoscopy or skin scraping can identify mites, eggs, or fecal material. Negative testing does not always exclude scabies, but objective confirmation is especially valuable in atypical, institutional, or crusted disease.
Map transmission
Prolonged direct skin contact is the main route. Review household, sexual, caregiving, and institutional contacts during the prior two months. Symptoms can be delayed in a first infestation.
Protect alternatives and complications
Atopic and contact dermatitis, insect bites, drug eruption, folliculitis, and other pruritic conditions can mimic scabies. Pain, pus, fever, severe crusting, or systemic illness needs another pathway.
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Lesson
Treat Classic Scabies as Whole-Body and Whole-Household Care
Permethrin 5 percent remains first-line from age two months. Oral ivermectin is off label, and spinosad has a distinct labeled scabies regimen from age four years.
- Permethrin 5 percent
- Oral ivermectin
- Spinosad
- Complete coverage
- Simultaneous contacts
Comprehensive coverage
Weight and pregnancy limits
Scabies directions differ from lice
Treat the network simultaneously
Apply permethrin comprehensively
Apply 5 percent cream over the prescribed body surface, including folds, under nails, between digits, buttocks, groin, and soles. Young children may require head and neck coverage. Reapply to hands if washed during the exposure and remove after eight to fourteen hours.
Use oral ivermectin accurately
For selected classic scabies, experts use two 200 microgram per kilogram doses with food, seven to fourteen days apart. This is off label, and safety is not established below 15 kg or during pregnancy.
Do not copy spinosad directions between indications
For scabies from age four, spinosad covers neck to toes, including soles, dries ten minutes before dressing, and remains at least six hours. Its ten-minute head-lice contact time is not the scabies regimen.
Treat contacts and recent items
Coordinate simultaneous contact treatment. Wash bedding, clothing, and towels hot and dry hot. Seal nonwashable items at least 72 hours to one week. Avoid direct skin contact until treatment is complete.
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Lesson
Escalate Crusted Scabies and Institutional Transmission
Crusted scabies has a massive mite burden, high contagiousness, and sometimes limited itch. It requires combined therapy, keratin management, precautions, and outbreak coordination.
- High mite burden
- Combined therapy
- Keratolysis
- Contact precautions
- Outbreak tracking
Mite burden can be massive
Severity guides repeated schedules
Reach mites beneath crust
Stop institutional amplification
Recognize the dangerous pattern
Widespread hyperkeratotic crusts, scaling, fissures, nail involvement, institutional exposure, immune compromise, neurologic disease, or inability to scratch should raise concern even when itch is limited.
Combine systemic and topical treatment
CDC describes oral ivermectin schedules of increasing intensity plus frequent permethrin 5 percent. There is no single consensus schedule, so severity and specialist protocol determine exact dosing.
Improve topical penetration
Keratolytic therapy on non-permethrin days may reduce thick crust and improve scabicide penetration. Monitor barrier injury, bacterial infection, hydration, temperature, and medication exposure.
Control the outbreak as a system
Use contact precautions, identify staff and residents with direct exposure, treat contacts in a coordinated window, manage linens and rooms, track completion, and notify infection prevention or public health.
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Lesson
Close the Loop on Safety, Failure, and Residual Itch
Product concentration, minimum age, body surface, pregnancy, lactation, weight, damaged skin, seizure risk, immune status, and caregiver technique determine safe exposure.
- Age thresholds
- Pregnancy narrative
- Postscabetic itch
- New lesions
- Failure audit
Treat neonatal and poorly examinable disease differently
Balance indication, evidence, and drainage reduction
Define a response window for every plan
Escalate whenever the pattern threatens vision
Use exact pediatric assessment and labeling
Do not stop after wax if impairment remains
Define a 48 to 72 hour checkpoint when infection is treated
Act on mastoid, neurologic, invasive, or sudden findings
Use age-specific labels and quantities
Reconcile every topical and systemic exposure
Do not rely on redness alone
Set targets, timing, and escalation
Individualize exposure
Name the actual systemic product
Confirm safe execution
Define the next decision
Prevent formulation errors
Use product-specific evidence
Hypersensitivity resolves slowly
Separate activity from recovery
Use exact age and formulation
Permethrin 1 percent for lice and 5 percent for scabies are not interchangeable. Spinosad begins at six months for lice and four years for scabies. Ivermectin lotion begins at six months for lice, while oral ivermectin has distinct off-label limits.
Use narrative reproductive reasoning
Retire pregnancy letters. Integrate product-specific human and animal evidence, infestation risk, route, surface area, duration, weight, alternatives, lactation exposure, and patient goals.
Explain residual itch before it happens
Scabies itch can persist for several weeks because hypersensitivity resolves slowly. New burrows, new papules, live mites, untreated contacts, or symptoms beyond the expected interval are more concerning for active failure.
Audit every failure
Reconfirm organism, product, concentration, amount, coverage, contact time, repeat timing, contact treatment, recent-item control, reinfestation, irritation, and resistance before adding or switching insecticides.
Quick check
Module test
Check the connections.
Each attempt draws 10 questions from the complete 112 question bank.
Each attempt draws a fresh set and rearranges the answer choices.
References
Current clinical foundation.
Lecture material was synthesized with the following contemporary guidance. Verify local policy and current guidance before applying clinical information.