Head lice are becoming resistant to some of the insecticides long used to kill them, experts have warned, as millions of children return to the classroom and come into close contact with classmates carrying the bugs.
One online pharmacy reported that sales of head lice treatments jumped by 57 per cent last September compared with other months, as the tiny, blood-sucking insects spread rapidly through schools.
Head lice live in the hair and on the scalp, where they feed, breed and lay eggs that cling stubbornly to strands, with their bites triggering relentless itching. Experts say treatments that once worked reliably can now fail because the insects have evolved resistance to insecticides such as permethrin and malathion.
British studies have found widespread resistance to both chemicals, prompting the popular description "super lice." The NHS now specifically advises against head lice products containing permethrin because they are unlikely to work.
How children catch head lice
Dr Ian Burgess, director of the Medical Entomology Centre, said lice have been around for as long as human beings. Contrary to popular belief, they cannot jump or fly, and instead crawl from one person's hair to another, meaning prolonged head-to-head contact is by far the most common way they spread. A louse can transfer from one scalp to another in as little as 30 seconds.
"Children pick them up from friends and siblings when playing, whether that be in the playground at school, in the park, at clubs, in the garden or at family social events," Dr Burgess said. He added that close physical contact, including head-to-head touching, is common among children playing together.
Although infestations often become apparent when children return to school in September, Dr Burgess said they may actually have picked up lice during the summer holidays, since it can take several weeks for an infestation to become obvious. Lice can spread via shared hats, brushes, pillows or towels, but experts say this is far less common, as the insects are adapted to living on the scalp and do not survive long once separated from it. The claim that head lice prefer dirty hair is a myth, according to studies, which show the insects have no preference for clean or dirty hair.
Spotting an infestation
The only sure sign of head lice is finding a live, moving louse in the hair. Adult lice are roughly the size of a sesame seed and greyish-white to brown in colour, while their eggs are even smaller and firmly glued to individual hairs, usually close to the scalp, particularly behind the ears and around the nape of the neck.
The easiest way to check is with a fine-toothed detection comb, used on wet or dry hair by working systematically from roots to ends. Itching, along with a tickling or crawling sensation, is often the first sign parents notice, and repeated scratching can leave small red bumps or sore patches. However, an itchy scalp alone does not mean a child has lice, and some infested people feel little or no itching. Dr Leila Asfour, of the British Association of Dermatologists, said treatment should only begin once a live louse has been found, and products should not be used preventatively.
Over-the-counter treatments
Dr Burgess said treatments generally fall into two categories: traditional insecticides that poison the lice, and newer "physical" treatments, often containing silicone-like substances, that kill the insects without conventional pesticides. Physical treatments have largely replaced insecticides as resistance has grown.
One pesticide-free option is Hedrin 4% Lotion, priced at £15.30 for 150ml at boots.com, which contains dimeticone, a silicone-based substance that coats lice and interferes with their ability to survive. It is applied to dry hair, left on for eight hours or overnight, then washed out. Dr Burgess said even products claiming to work in one treatment should be repeated after a week, with checks continuing over the following week to ten days, since surviving eggs can hatch and restart the cycle.
Wet-combing is 'most effective' method
Many experts consider wet combing one of the most effective ways to remove head lice, since the insects cannot develop resistance to being physically removed. The method involves washing the hair, applying conditioner, then working through the head in sections with a fine-toothed detection comb from roots to ends, wiping or rinsing the comb after each stroke to check for lice.
A study by the London School of Hygiene & Tropical Medicine found that systematic wet combing cleared head lice in 57 per cent of cases, compared with just 13 per cent among children given certain insecticide treatments. The NHS recommends wet combing on days one, five, nine and 13, with a further check on day 17 to confirm the infestation has cleared. Dr Burgess recommends a comb with flat-faced teeth no more than 0.3mm apart, narrow enough to catch newly hatched lice. Everyone in the household should be checked, and anyone with live lice treated at the same time to prevent the insects passing back and forth.
No need to wash soft toys
Parents do not need to strip beds, scrub sofas or freeze teddy bears, experts say, because lice need regular blood meals and the warm, humid conditions of the scalp to survive, and struggle once separated from their host.
"You don't need to do any special cleaning, you don't need to boil your sheets and nothing needs to go into a freezer," Dr Burgess said. "Any louse that was stupid enough to climb off on to the bed while you're asleep will dehydrate within eight to 12 hours." Because lice spread mainly through direct head-to-head contact rather than bedding or furniture, a major household clean is unlikely to help; time is better spent checking and treating household members.
Can head lice be prevented?
Pharmacy shelves carry preventive sprays, shampoos and essential oils such as tea tree, rosemary and peppermint, but there is little good-quality clinical evidence that any reliably prevents infestation. "Short of having no friends, it's not possible to prevent your child getting lice," Dr Burgess said. "It's a natural part of social development."
The NHS says children with head lice do not need to be kept off school once an infestation is found. Tying back long hair may reduce opportunities for hair-to-hair contact, though it offers no guarantee against lice. Experts say regularly checking a child's hair with a detection comb, particularly when lice are known to be circulating among friends or classmates, is the best way to catch and treat an infestation early.
