When children go back at school at the start of the new academic year, they can often unwittingly return with some unwelcome homework for their parents...

AT THIS TIME OF YEAR it is common for pharmacy staff to be asked about treating head lice. While these parasites do not represent a serious health problem and rarely cause any discomfort greater than an itchy scalp, customers often find them embarrassing. As they can spread quickly from one person to another, head lice should always be treated promptly.

How are head lice picked up?

Head lice are tiny, grey-brown wingless insects about the size of a sesame seed that live in human hair and feed on blood by biting the scalp. They crawl from one host to another and are usually picked up by head-to-head contact. They are particularly common in children of primary school age, who have greater levels of contact with their peers, and are commoner in girls than boys. Infestations often occur at the start of each school term.

What are the signs of an infestation?

Many cases of head lice infestation are symptomless, especially in the early stages. The main indication of an infestation is an itchy scalp that is caused by an allergy to louse saliva or faeces. The allergy develops slowly over weeks or months and by the time it is noticed there may be many lice living on the head. Parents might also spot small red bites on the scalp or black specks (louse faeces) on pillows or clothes. The only way to know for sure if someone has an infestation is to find a live louse on their head.

“People often refer to head lice as ‘nits’ but these are actually the empty egg casings of the lice, which are glued to hair shafts,” says Michael Stewart, Numark’s information pharmacist. “They are difficult to remove but are not a sign that someone has an active infestation – they could be left over after successful treatment.

“Being so small, head lice can be difficult to spot just by looking at the hair. A detection technique needs to be used called dry combing, which should take around five minutes depending on the length and thickness of the hair. The number of lice found can vary greatly. There are typically 15 or fewer, but finding just one live louse will require treatment.”

What are the pros and cons of the different treatment methods?

There are a number of different products available for treating head lice. Pharmacy staff can help parents choose which one to use by explaining how the various products work and how they should be used.

Chemical insecticides

Malathion 0.5% aqueous liquid: Over the years head lice have become resistant to chemical insecticides and currently malathion 0.5% aqueous liquid is the only one recommended in the UK for treating head lice infestations. It is not recommended for children under six months of age but is safe to use on people with asthma or skin conditions such as eczema. The drawback of this lotion is that it must be allowed to dry naturally and left on the hair for at least 12 hours or overnight in order to be effective. A second application is needed after seven days.

Elizabeth Brunton, deputy director of Insect Research and Development Ltd at the Medical Entomology Centre in Cambridgeshire, says there is documented evidence of resistance to malathion but, as resistance patterns vary across regions of the UK, its effectiveness will be better in some areas than others.

Physical insecticides

Physical insecticides kill lice with a physical mode of action. The insects are unlikely to develop resistance to these products. There are three main active ingredients currently in use – dimeticone, isopropyl myristate and octanediol.

Depending on the preference of the individual or parent and on the treatment history, head lice can be treated with a lotion, mousse or spray. Some of the newer products on the market kill eggs as well as lice, work quickly and so do not need to be reapplied, making them more convenient to use.

• Products containing dimeticone are widely considered to be a first-line alternative to chemical insecticides. The active ingredient is a silicone oil, which coats the lice, immobilises them and disrupts their ability to pass water and get rid of excess waste. These products are suitable for anyone over the age of six months and are safe to use on people with skin conditions and asthma. Treatment must be repeated after seven days

• There is a product on the market containing an ingredient called penetrol (Hedrin Once), which allows dimeticone to enter head lice eggs and kill them before they hatch, removing the need for a second application. This product can therefore be effective with a single, 15-minute treatment

• Isopropyl myristate and cyclomethicone solution are similar to dimeticone in that they work by suffocating the lice. The solution is applied to dry hair and left on for at least 10 minutes before combing through with a fine-toothed comb to remove the lice. Treatment must be repeated after seven days. These products are not suitable for asthmatics because of a lack of study data in this patient group

• Octanediol dissolves the waxy protective coating on lice, which causes them to dehydrate and die. This treatment does not kill the eggs so a second application is needed. Octanediol is waterbased so is likely to appeal to customers who dislike the oiliness of some other physically acting preparations since it is easy to apply and rinse off

• A new product on the market containing isopropyl myristate and isopropyl alcohol, Vamousse, kills head lice and their eggs in one 15-minute treatment. The formulation works by dissolving the waxy exoskeleton, leading to water loss and death by dehydration.

I’ve had people trying to get rid of head lice by putting petrol, Vaseline and washing up liquid on their children’s hair

Wet combing

The wet combing technique can be used to treat head lice infestation and is useful for parents who are worried about using a lotion or spray on their children. If done properly wet combing is effective at removing lice but is very time-consuming, with each session taking up to an hour. To be effective, wet combing must be undertaken twice weekly for a fortnight or longer if live lice are still present.

Pregnant women should be advised to use either the wet combing method or 4% dimeticone lotion, which is licensed for use during pregnancy and breastfeeding.

Why does treatment sometimes fail?

Treatment may fail because:

• The diagnosis of a head lice infestation may have been incorrect – has a living, moving louse been seen?

• The customer may not have followed treatment instructions correctly

• The lice may have been resistant to the chosen treatment

• The customer may have picked up a new infestation immediately after the treatment was completed because contacts may not have been identified and treated at the same time

• A report of an itchy scalp could be scalp irritation or a psychogenic itch.