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Head Lice Infestation

Head Lice Infestation

11 August 2023

Causative agent

Head lice, Pediculus humanus capitis, are tiny parasites (up to 3mm long) that only live on the human head. They are usually found on the hair, most often around the hairline behind the ears or near the neck, and occasionally on the eyebrows or beard.

Clinical features

The most common symptom is itching and tickling sensation on the scalp. Excessive scratching may cause bleeding or sores on the scalp, increasing the risk of skin infection.

Under careful inspection, eggs of head lice can be found near the root of the hair. They are different from dandruff. Eggs are usually white or yellow in colour, oval in shape and firmly attached to hair shafts; while dandruff is flaky and loose enough to fall off easily.

Mode of transmission

The lice move by crawling; they cannot jump or fly from one hair to another. The main mode of transmission is through head-to-head contact with an infested person, and less commonly through sharing of personal items such as combs, hats or hair accessories. Anyone may catch head lice. However, young children are of higher risk because they often come into close contact with one another while playing.

Incubation period

The life cycle of head lice goes through 3 stages: the eggs, the nymphs and the adults. The eggs hatch in 7 - 10 days; the nymphs take 7 - 12 days to become adults, which can reproduce in huge numbers. Both nymphs and adults feed on human blood. Adult lice can live up to 30 days but usually die within 2 days once they fall off from the human body. Persons with head lice are infectious as long as the eggs or lice are alive.


  • If you suspect head lice infestation, seek medical advice immediately.
  • Apply medicated lotion or shampoo according to doctor’s prescription to kill the lice. Rinsing of hair after medication application should be done over a sink rather than during a shower or bath to limit skin exposure, and with warm water instead of hot water to minimise skin absorption.
  • Use a fine-toothed comb to remove the lice and eggs. Remember to discard the eggs properly. Vacuuming furniture and floors can remove an infested person’s hairs that might have viable eggs attached. Disinfest combs and brushes used by an infested person by soaking them in hot water (at least 54°C) for 5–10 minutes.
  • Machine wash and dry clothing, bed linens, and other items that an infested person wore or used during the 2 days before treatment using the hot water (at least 54°C) laundry cycle and the high heat drying cycle. Clothing and items that are not washable can be dry-cleaned or sealed in a plastic bag and stored for 2 weeks before reuse.
  • Wear gloves when making contact with patients.
  • Wash hands thoroughly before and after contact with the infested person. Wash hands with liquid soap and water, and rub for at least 20 seconds. Then rinse with water and dry with a disposable paper towel or hand dryer.
  • Screen household contacts and close contacts of infested people for head lice and treat them at the same time accordingly.


  • Keep both hands clean and perform hand hygiene properly.
  • Avoid close contact with infested people, especially head-to-head (hair-to-hair) contact.
  • Do not share personal items such as combs, hats, hair accessories, towels or pillows.
  • Check hair regularly for signs of head lice infestation.