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Diagnosis of head lice

By Dr Ananya Mandal, MD

Head lice infestation, caused by tiny insects or head lice, are usually diagnosed based on clinical findings.

Parents and teachers might discover the nits or eggs or adult lice in the child’s hair.

In the case of head lice, a school nurse usually discovers the infestation on routine checks.

Adults in the family may also be checked for head lice.

Symptoms of head lice

Commonest complaints are itching especially at nights.

Children may have difficulty sleeping due to the severe itching at night when lice are feeding.

The scalp, the back of the neck, and behind the ears are commonly affected sites.

Sometimes it may be two months before lice is detected in a child. Children may also have eyelash and eyebrow involvement.

Diagnosis of head lice

Diagnosis of head lice infestation includes observation of eggs or lice, examination under a microscope and so forth. (1-4)

Observation of eggs, nymphs or adult lice

Observation of eggs or nymphs, or mature adult lice.

Since it is difficult to detect a live louse as they can move rapidly through dry hair, wetting the hair may be used. Wet hair makes the louse unable to move.

The hair needs to be washed and conditioner has to be applied before combing.

They can then be detected using a special fine toothed comb. The comb has a tooth spacing of less than 0.3mm. This can trap the adult lice as well as the nymphs.

This method is called detection combing.

Wet detection combing is done on all individual sections of hair methodically and may be repeated on wet hair after the conditioner is washed off.

The use of a magnifying glass may help. Examination under sunlight or full light is needed to identify the lice or nits over the scalp.

Examination under a microscope

Lice may also be trapped using a piece of transparent adhesive tape or cellulose tape over the infested area.

As the lice get stuck to the tape, it may be removed and examined under the microscope.

Adult lice are 3-4 mm long with 3 pairs of legs and narrow mouthparts. Nits are approximately 1 mm in length. They may appear like a capsule or a flask.

Wood lamp examination

A Wood lamp examination of the infested area shows yellow-green fluorescence of lice and nits.

Ruling out other conditions

Other conditions that mimic head lice infestation have to be ruled out.

There are hair casts or pseudonits that look like nits. Actually these are ring-like remnants of the inner root covering of the hair follicle.

These pseudonits, unlike actual nits, move freely along the hair fiber.

Head lice nits may also appear as dandruff. Unlike dandruff where the skin flakes off, the nits stay put.

Sometimes fungal infections may appear as nits.

Hair spray gels and droplets may also appear as nits.

Conditions that need to be considered include skin infections (boils etc. called impetigo or folliculitis), insect bites, scabies (another skin infestation with an insect), acne and psychological conditions where the person feels he or she has bugs or insects over the body.

Edited by , BA Hons (Cantab)

Further Reading

What is head lice?
Head lice Causes
Head lice Symptoms
Head lice Treatments

Last Updated: Jun 27, 2012

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