What and Why?
The human head louse is a very resourceful insect that lives 5-6 weeks, exclusively in human hair. It starts life as an egg the colour of your scalp, attached to a hair very near its root. The hairs over your ears, at the nape of your neck and under your fringe are favoured because they keep warmer; the eggs need to incubate at 30-31oC for a week, by which time your hair has grown 3mm. The pearly white nit is much easier to see, clinging to your hair as far from your scalp as it has grown since the egg was laid — about a centimetre for every month.
Meanwhile the louse matures within ten days and mates; four out of five are female. Each then lays six to eight eggs daily for the rest of her life. She moves quickly through hair close to the scalp, using six large claws to hang on firmly. You have to be quick to spot one, because they are sensitive to light and avoid exposure to it. They do not fly or jump, but are quick to transfer to another head whenever close enough contact occurs; a few seconds is enough. One louse can visit several heads in a day if she gets the chance!
A louse feeds several times a day from blood vessels in your scalp with its long retractable mouth, injecting a little anaesthetic saliva as it probes. This prevents you discovering the insect immediately but gives it away in the long run; sensitivity to these accumulating injections makes you itch, after two months. If you do not then deal with it, or are constantly reinfested, after about a year you become much more profoundly sensitized. Your muscles become uncomfortable, especially in your legs, and you feel generally unwell — ‘lousy’ in fact. A ‘nit-wit’ is a child so affected that he cannot concentrate or think straight!
Children in nursery and infant schools are the main reservoir of head-lice, girls more especially; but short hair is not an advantage. The insects prefer a clean scalp, so frequent washing does not protect you. Indirect transfer never occurs; only an insect already half dead would drop onto clothing.
Although lice may at times run wild through whole schools, infesting practically every pupil and many of their families, infestations are nowadays seldom prolonged; school nurses react urgently to any reported outbreaks. But they rely increasingly on shampoos and lotions containing one of two potent insecticides — Carbaryl and Malathion — to kill the lice they find. Consequently lice are becoming resistant to insecticides, just as bacteria have decoded many antibiotics. The insecticide is easily destroyed by heat or sunlight, so that the dose actually received may be less than intended; this helps give the insect time to develop resistance. We had better re-explore the simple measures we relied on for centuries, which cost little and are harmless.
What can I do?
Advice to maintain and maximise health
1. Grooming your hair daily with a strong undamaged comb or a couple of stiff brushes is the best simple hygienic protection. That makes life dangerous for any lice. A damaged claw makes them less functional; they stop laying, feed less well, and perish.
2. Search your children’s hair for nits every time you wash it, at least once a week. To spot insects part the hair quickly with a comb, and move the parting systematically across the scalp; watch for the louse retreating fast!
3. Comb: Obtain from the chemist a fine-toothed metal comb, designed to strip eggs and nits from hair; every family should have one. Whenever you discover lice or nits wash or rinse your hair and groom it thoroughly with an ordinary comb. Work systematically over your scalp from the scalp upwards as far as your nits are visible. Some combs have teeth cut square on one side and bevelled on the other: the first does the stripping, so should face away from your scalp.
4. Herbal remedies: Rue tincture (Ruta graveolens) makes an excellent deterrent to lice, which is perfectly safe for people. Apply rue tincture diluted one-in-three, or a strong tea made from dried leaves, as a lotion in the evening; wash it off the following morning. An alternative lotion is Sabadilla tincture, diluted one-in-ten with water. Homoeopathic Nat mur 6 can be taken four hourly through an outbreak, alongside either lotion.
5. The insecticides Carbaryl and Malathion are used medicinally in lotions and shampoos at 0.5% concentration, to kill lice and eggs outright. We are assured that even this rather high strength is safe but have never been shown evidence from safety tests under these conditions of use, so be wary. If you decide you have to use them make it once only, following the instructions meticulously; note that heat, sunlight and chlorine destroy them very easily. Afterwards, depend on harmless lotions and weekly vigilance.
6. If you do decide to use an insecticide lotion, check first with your doctor or health visitor. Not only can you get supplies without charge, but they will ensure that you choose the material in current use. There is a national policy in operation to alternate Carbaryl and Malathion systematically, so as to reduce the risk that insects will become immune to either.