Head Lice


Human lice infestation (pediculosis) is a continuing problem worldwide. One of the major reasons is increased resistance to pharmacological treatments due to incomplete eradication of colonies. The life cycle of lice has to be interrupted at various stages to ensure that after treatment has commenced, the condition is cured. If this is not achieved, repeated exposure to toxins will favour resistance with infestations becoming more difficult to treat pharmacologically.

The most susceptible stage in the lifecycle of the louse is the nymph. Emerging from the protective nit (egg), regular registered toxins will most likely kill it. As the louse grows, the exoskeleton rapidly develops becoming more impenetrable. Moulting (stage one, two and three) takes place three times before sexual maturity when most susceptible to toxins. It is unlikely that all adult lice are eradicated with a single chemical treatment and thus necessitates a treatment program.

Generally by the time head lice are discovered, eggs have already been laid. These eggs are called nits and are laid on a hair close to the scalp in temperate climates (ensuring a favourable environment for egg development). As the hair grows, the distance from the scalp gives an indication of the time it's been on the hair. It is attached with a strong adhesive glue (keratin type substance) and difficult to identify or remove; treating these are impractical and less successful. Nits form a very effective protective shell and are unlikely to lose viability with chemical treatment. Continual hatching (on a daily basis) as well as egg laying takes place in advanced infestations. With treatments only effective during certain stages in the life cycle, it is clear that repeated treatments are necessary to achieve complete eradication.

Credit: headlicelifecycle.com


Physical removal of lice and nymphs become more important with increased resistance. Individual lice that are not killed by toxin become paralysed for a limited period during and after exposure. During this time clinging to hair (with the hook-like claw protruding from the legs) becomes ineffective and physical removal becomes easier. Combing with a fine toothed lice comb during treatment removes lice easier. Close observation should be kept on removed lice as the physical size of removed ones should get smaller with consecutive treatments. After three weeks of treatment (every fifth day) the colony will most likely be eradicated.

Treating head lice with permethrin 5% lotion (off-label)

Although not registered for this indication, the established safety profile of permethrin 5% application makes it suitable for the treatment of head (and body) lice infestations. (To illustrate safety, this application is applied over the whole body and left on for twelve hours for babies 2 months and older for the treatment of scabies).

Extract from Virginia Dept of Health: Pediculosis (Head lice) - Management August 2008:

"Note, you should not use over-the-counter medicated lice treatments for children less than two years old. Instead, remove the nits and lice only by using a fine-tooth comb on the child's hair after regular shampooing every day for two weeks. If necessary, permethrin 5% is available by prescription for use in children over two months of age - consult with your paediatrician".

Harvard school of Public Health - HEAD LICE INFORMATION

Statement from Richard J. Pollack, PhD
"Some physicians treat apparently resistant infestations with a prescription-strength pyrethroid (3 - 5%) preparation normally meant for treating scabies infestations".

As nits are unlikely to lose their viability with treatment, more than one treatment is necessary to eliminate nymphs before they reach sexual maturity and start reproducing.

Treatment regime:

According to the National Department of Health, the treatment regime for lice with permethrin 5% is as follows (5.7.1.1 head lice):
  1. Apply permethrin 5% lotion to towel-dried or dry hair - comb into hair repeatedly with a normal comb until scalp is covered completely
  2. Comb until hair is completely detangled and start combing with fine lice comb - divide scalp into sections to cover all areas and comb away from scalp as indicated. The lotion has a conditioner type texture and facilitates combing and removal.
  3. Rinse lice comb in a white bowl filled with hot water between hair strokes to identify removed lice, or detach on white tissue paper. Paralyzed and dead lice will present as dark spots (like ground pepper) in the white bowl or on tissue.
  4. Take note of the physical size of removed lice and nymphs as the size should get smaller with consecutive treatments
  5. Keep on combing with fine lice comb for half an hour while rinsing or wiping comb frequently
  6. Permethrin 5% lotion is safe and can be left in the hair for up to one hour
  7. After combing, rinse hair with lukewarm water and wash permethrin 5% lotion out with normal shampoo - more than one foaming might be needed.
  8. This procedure should be repeated every five days for three weeks
  9. Frequent inspections should be carried out thereafter to detect new infestations early




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