Head Lice


Parasites predominantly infesting children. The lice live on the head, feeding on host blood. They can cause itching. Lice lay eggs which they attach to hair shaft, commonly behind the ears and at the back of the head. Nits are hatched eggshells. Lice can only survive off the scalp for a few hours. Incidence is extremely low in children with shaven hair styles (1mm or less) and those that use copious amounts of hair gel. Head lice are commonly seen between the ages of 4 and 12 with a peak incidence in 7-8 year olds. Mothers of school children are also commonly infested.


Definitive diagnosis is made if there are living lice present

Use a louse-detector comb to find lice in the scalp

Examine all the family (including adults) and school classmates for non symptomatic cases. These will reduce re-infestation

Nits are evidence of past but not active infestation.


  • Should only be started if lice are found
  • Lotions are much more effective than shampoos
  • In order of preference:
    • Try regular combing – at least nightly for 2 weeks with a head louse comb on wet hair. Hair conditioner is optional. A cure or acceptable control (low level of infestation) may be obtained
    • 0.5% Malathion lotion. Available over the counter. Apply to dry hair, must be left on for at least 12 hours to kill the lice. Repeat after one week. If lice still present then treat with an alternative chemical lotion because drug resistance is common to Malathion
    • 1% Permethrin cream rinse or 0.2% or 0.5% Phenothrin lotion/liquid. Available over the counter. Permethrin is probably more effective. Apply after shampooing hair and leave on for 10 minutes. Repeat at 7 days. If lice still present then treat with an alternative chemical lotion because drug resistance is extremely common to both chemicals
    • 0.5% or 1% Carbaryl lotion/liquid. Apply to dry hair and leave on for 12 hours. Prescription only medication. Repeat after 7 days. No evidence of significant drug resistance. Regular use not recommended because of possible carcinogenic risk. Suggest no more than 4 treatments a year

Additional notes on treatment

  • Scalp psoriasis and eczema can be exacerbated by head lice and should be treated with standard scalp preparations in tandem with head lice treatments
  • Scalp fungal infections and impetigo can also be a consequence of head lice. Again, these should be treated with standard preparations in tandem with head lice treatments. Systemic absorption of anti head louse chemicals will be slightly increased in these situations but this is not harmful
  • Bed clothing etc need not be changed
  • Cutting or tying back hair does not help

Content by Dr Íomhar O' Sullivan 07/06/2005. Reviewed by Dr ÍOS 03/07/2007. Last review Dr ÍOS 31/08/22.