We humans think we sit on top of the food chain, but the pediculosis capitis mite – the head louse – sits above us, on the top of our heads.
The head louse is a small, wingless insect that feeds on human blood. It moves around our scalp swinging from hair to hair, mates and then lays its eggs in special cases (nits) attached to the base of our hair fibres.
Around 13% of school-age children are thought to have head lice at any given time, with girls more than twice as likely to be infected than boys.
Pediculosis capitis has been around for millions of years. But homo sapiens are the only known host for the modern day head louse. The chimpanzee has a similar but genetically distinct mite, as do most mammals.
The head louse is usually relatively harmless and more of a nuisance than a disease.
But in World War One, head lice were a major cause of sickness and, occasionally, death. Because soldiers were wearing the same uniform for days, lice were able to migrate off the scalp and inhabit the seams of the uniform. These lice became the vector for Bartonella infection, which caused trench fever. Three famous sufferers were authors JRR Tolkien, AA Milne and CS Lewis.
Head lice are very itchy and scratching can lead to secondary infection with golden staph, a potentially serious illness.
That being said, the biggest problem most people have with head lice is finding a way to get rid of them. Over the past 50 years, we have seen one insecticide after another lose effectiveness as the lice find a way to adapt, evolve and become resistant.
For the past ten years, the most reliable way of getting rid of head lice has been the application of a thick film of conditioner to the hair and daily combing to manually extract the lice. If you have a daughter with long thick hair, this procedure can take half an hour a day. If you have got two or three daughters infected with lice, the treatment process quickly becomes a nightmare.
How do you catch head lice?
A female louse will lay between three and eight eggs per day. The eggs attach to the hair fibres within 1.5 centimetres of the scalp and rely on the warmth from the head to hatch.
Head lice do not have wings so they cannot fly, and their short stumpy legs mean that they cannot jump from head to head. They can only crawl.
People get head lice from direct, head-to-head contact with another person who has head lice. This can happen when people play, cuddle or are close together. Head lice are most common among children and their families. If your family has head lice, tell anyone who has had contact to check their family.
In general, there is no need to treat the whole family unless they also have head lice. There is no evidence that you need to clean the house or the classroom or that either changing the bed linen or pillow cases helps.
Finding head lice
Half the people who have head lice never scratch their head, so itching is not a reliable sign. Lice can be hard to spot because they move quickly.
If you suspect you or a child has head lice, the easiest and most effective way to find them is to use the conditioner and comb treatment. Massage 50 millilitres of conditioner into a dry scalp. Then comb through the scalp with a broad-tooth comb to detangle the hair. This makes it difficult for the lice to grip onto the hair.
Then, using a very fine tooth nit comb, divide the scalp into six sections and comb through from root to tip, wiping the conditioner from the comb onto a paper towel or tissue to see if there are any lice, and remove them if there are.
Treatment for head lice
Two treatments are available for use at home without prescription and one is available only on prescription from your doctor or dermatologist.
The non-prescription treatments are the conditioner and comb method as described above, or to use an insecticide. For the conditioner and comb method, you’ll need to repeat it at least once a week until you’re no longer extracting any lice.
A large number of insecticide products are available over the counter in pharmacies without prescription. Take care when using these products if you’re pregnant or breastfeeding or if the child is less than 12 months old.
No topical insecticide treatment kills 100% of the eggs so you’ll need two applications, seven days apart. If the insecticide works, the lice will be dead within 20 minutes. If the lice are not dead, the treatment has not worked and the lice are resistant to the product.
Tablets for head lice
If the initial non-prescription treatments have failed and you’re still removing live lice with the conditioner and comb, see your doctor for a referral to a dermatologist for specialist treatment.
Ivermectin is a prescription medication available either as a tablet to take orally or a lotion to apply to the scalp.
While a single dose will stop the lice in their tracks, it should be repeated after seven days to ensure any unhatched eggs are also killed.
For children too young to swallow a tablet, the ivermectin can be formulated as a syrup. For very young children, pregnant women and women who are breastfeeding, the ivermectin can be used as a lotion in the scalp.
Ivermectin has been available in Australia for the past 15 years. But while it was added to the pharmaceutical benefits schedule (PBS) last year, it’s only subsidised to treat scabies (mites that burrow into the skin), so you may have to pay full price when filling scripts for head lice.
Rodney Sinclair does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.
Authors: The Conversation