Head lice

head lice · nits · pediculosis capitis · headlice

Diagnosed only by finding a living louse - eggs alone do not justify treatment.

DISCHARGEBand C

Red flags

Secondary bacterial infection of the scalp with spreading cellulitis or lymphadenopathy
Extensive infestation with anaemia in a very neglected presentation - consider a safeguarding assessment of the wider picture
Repeated treatment failure - usually incorrect application or untreated contacts rather than resistance
Treatment being given repeatedly with no louse ever found

Recognise

On light skin

Itchy scalp with excoriation, live lice visible on wet combing, and whitish egg cases firmly attached to hair shafts near the scalp.

On brown and black skin

The louse itself and the egg case are the findings, and both are objects on the hair shaft rather than changes in the skin, so pigment is largely irrelevant to the diagnosis. Two practical points do differ: scalp excoriation and secondary infection may not appear red, and detection combing is harder in tightly coiled or braided hair, where wet combing with plenty of conditioner, worked in sections, is more reliable than inspection. Do not let difficulty combing become a reason to treat without confirmation.

In any skin tone

A living, moving louse must be found - this is what confirms the diagnosis
Egg cases attached firmly to the hair shaft; empty white cases further from the scalp indicate a past infestation, not an active one
Itch is variable and many people have none
Detection combing on wet, conditioned hair is more sensitive than looking
Ask about affected household members and classmates

Distribution

Scalp, particularly behind the ears and at the nape of the neck.

Photographs

A single nit cemented to a hair shaft, seen under the microscope. The teaching point survives the magnification: the egg case is glued to on — A single nit cemented to a hair shaft, seen under the microscope. The teaching point survives the magnification: the egg case is **glued to one side of the shaft and will not slide along it**, which is how a nit is told from dandruff, hair casts or product residue - those move freely when you run them between finger and thumb. Nits close to the scalp suggest active infestation; ones several centimetres out have grown away with the hair and may be long dead. **Diagnosis needs a live louse found by wet combing**, not nits alone. A magnified view, not a bedside one: no openly licensed clinical scalp photograph survived provenance checking.
Fitzpatrick II (Fitzpatrick type estimated from the photograph, not stated by the source) · Commons user Wikitorre92 · Wikimedia Commons - Liendre adherida a pelo.jpg · CC BY-SA 4.0

Provenance for every photograph in this library: image licences. How much of the corpus still has no darker-skin photograph: skin tone coverage.

Mimics

Scabies, including crusted scabies — Also an itchy infestation spreading in households, but with an entirely different distribution
Tinea capitis and kerion — Scalp scale with hair loss and lymphadenopathy is fungal, not lice, and needs oral antifungal treatment
Atopic eczema and infected eczema — Seborrhoeic scale can be mistaken for egg cases; scale flicks off the hair, egg cases do not

What to do in the ED

Confirm with a living louse before treating. Treating on the basis of egg cases alone is the commonest error and leads to unnecessary repeated treatment
Treat with a physical insecticide such as dimeticone, or by wet combing, under local policy. Four groups are not a free choice: in pregnancy or breastfeeding, in children aged 6 months to 2 years, and in asthma or eczema, CKS puts wet combing or dimeticone 4% lotion first - in those groups it is not a free choice between products. Shampoos are not recommended: they are diluted too much and have too short a contact time to kill eggs
Repeat the treatment after the interval specified for the product, to catch lice hatching after the first application
Check household contacts and treat only those with live lice found
No exclusion from school is required - children should not be sent home for head lice
Explain that empty egg cases remain attached as the hair grows and do not indicate ongoing infestation

Disposition

DISCHARGE

Treat and discharge. This rarely needs an ED attendance at all, and reassurance plus correct technique is the intervention.

Safety-netting

Only treat people in whom you have actually found a live louse. Repeat the treatment as directed to catch newly hatched lice. The white egg cases stay stuck to the hair as it grows and do not mean the lice are back. Your child does not need to stay off school. Return if the scalp becomes sore, weeping, crusted or swollen, or if there is a fever.

Sources

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