Head lice treatments and advice

Head lice can affect people of any age but children between the ages of four and 11 years are the most frequently infested. Surveys in UK schools have found between 4 and 22 per cent of children are affected. Girls are more commonly affected than boys (this may be because girls often huddle together when playing) and children living in urban areas are more frequently infested than those living in rural areas. Although a common reaction to head lice is revulsion, it is worth remembering that a head lice infestation is a minor irritation — it rarely causes physical problems and head lice are not known to be vectors for infectious diseases. Children who are found to have head lice do not need to be kept away from school — by the time the infestation is diagnosed it will have been present for several weeks. If left untreated, however, the numbers of lice increase and can cause severe itching and scratching, which can then lead to a secondary bacterial infection, such as impetigo. The severity of infestation can vary but, in typical cases, about 10 lice can be found on a head. In addition, allergy to louse faeces can result in a rash on the back of the neck and behind the ears. Life cycle The louse is an external parasite of warmblooded animals (ie, birds or mammals), spending its entire life cycle on them. Head lice (Pediculus humanus capitis) live on human scalps. They cling to hairs close to the head, typically behind the ears or on the nape of the neck. They are rarely found in other hairy areas, such as eyebrows or eyelashes. Mature lice are about 3mm long and can be beige, brown or blackish, often blending in with the surrounding hair. Fertilised females can lay between five and 10 eggs each day. These oval, yellowish-white eggs are glued singly to hair shafts.After about seven days, the egg hatches, leaving an empty egg case or “nit” stuck to the hair. Young lice (nymphs) are white and smaller than adults. Over the next six to 10 days, nymphs moult three times and grow into mature lice (see Figure on p186). Head lice feed four to five times a day, piercing the skin and sucking blood from the host’s scalp.