Dr Caitlin: Head Lice Are Not Nice

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Dr Caitlin O’Connor of St Brendan’s Park Medical Centre, looks at the problem of head lice which can occur when children go back to school…

Head lice are tiny greyish-brown wingless insects that are about the size of a sesame seed when fully grown.

They have six legs that end in hook-shaped claws that grasp the hair very tightly until they are either dead or physically removed from the hair.

They cannot jump, hop, fly or swim, but they can crawl very fast. Direct contact is the route of transmission for head lice. Transmission from pets does not occur. Usual infestations contain around 30 lice per head.

They can only survive in a warm and humid environment, so they tend to stay close to the scalp where body heat and natural sweating maintain the ideal temperature and humidity.

Continued below…


During the lifecycle of lice, the female louse lays eggs (oval and yellow white), called nits which can be found attached to the hair shaft. Nits attach to the hair shaft close to the scalp or body-nits, which resemble dandruff, are attached with a water-insoluble, glue-like substance that makes them difficult to remove.

After 6-10 days, the nits hatch as nymphs (immature lice) – nymphs become adults in 10 days. Adult lice live for approximately 30 days on their human hosts.

Head lice are parasites that feed by taking regular blood meals from the human scalp. Before they feed, they inject a substance into the scalp to stop the blood from clotting before they have finished feeding.

Only about one third of people will have an itchy scalp – this is due to an allergic reaction to the substance the lice inject before feeding. Itching is usually a sign of a prolonged infestation, probably at least 3 months old!

You may see nits, or empty egg cases, in the hair. You may see small black specks on the pillow or if you comb the hair over a sheet of white paper.

If you wet the specks and they turn a reddish-brown colour, these are louse droppings. A very heavy infestation may be seen by a simple visual inspection of the scalp, but for lighter infestations, detection combing is needed in order to find a live moving louse.

Treatment options

All family members should be investigated for active lice infestation and those infested must be treated simultaneously. Head lice treatments should only be used when an infestation has been confirmed by the presence of a live moving louse.

As it’s very difficult to kill or remove unhatched eggs, some proprietary treatments must be used twice, seven days apart even if you think the lice have gone after the first treatment.

Insecticide treatments

These contain an active ingredient, an insecticide, also described as a pesticide. Treatment times vary greatly from 10 minutes up to 12 hours.

Apply treatments to clean hair without conditioner or styling products. Some insecticides remain in the hair to a degree after being rinsed off, and can continue to act on hatching lice, so avoid washing the hair between the first and second applications, and for several days after the second application.

Non-insecticide treatments

You may prefer to use a treatment that does not contain an insecticide. Some of these contain essential oils although there is no strong evidence that these are effective in clearing head lice infestations.

Non-insecticide treatments do not have any effect on the eggs, so a second application after seven days is essential. There are now some non-insecticide treatments, which are capable of eradicating lice by suffocating them.


This method physically removes the lice from the hair by intensive and methodical combing with a fine-toothed comb. To do this successfully you must comb the hair in sections.

This must be done every four days until all the eggs have hatched and all the lice have been removed. This method is only suitable for those who have the time and determination to carry it out properly, and is not really suitable for very young children.

Vigorous brushing will not break the legs of the lice and kill them. Lice can feed perfectly well with a couple of legs missing.

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