Head lice are transmitted by close head-to-head contact with someone who has head lice. The lice cannot fly, jump or swim, but they can climb from one hair to another, this is why children are often affected.

A head lice infestation is not the result of dirty hair or poor hygiene. Head lice can affect all types of hair irrespective of its condition and length. Head lice only affect humans and cannot be passed on to animals or be caught from them.

Head lice often cause the scalp to itch, although this is not always the case. Itching is not caused by the lice biting the scalp but by an allergy to the lice. In some cases of head lice, a rash may appear on the back of the neck. This is caused by a reaction to louse droppings.

Looking for head lice

Head lice are difficult to detect on the head, even when the head is closely inspected. Unhatched eggs or nits (empty eggshells) alone are not enough to diagnose an active head lice infestation.

In order to confirm an active infestation, a louse must be found through a reliable method, such as detection combing. Detection combing can be used to check more accurately for head lice. 

Detection combing

Detection combing can be carried out on dry or wet hair, but wet combing is more accurate because lice remain motionless when they are wet.

Detection combing involves using a special fine-toothed head lice comb that you can buy from your local pharmacy. The comb has a tooth spacing of less than 0.3mm to trap the smallest lice.

Wet detection combing

  • Wash the hair using ordinary shampoo and apply ample conditioner, before using a wide-toothed comb to straighten and untangle the hair.
  • Once the comb moves freely through the hair without dragging, switch to the louse detection comb. Make sure that the teeth of the comb slot into the hair at the roots with the bevel-edge of the teeth lightly touching the scalp.
  • Draw the comb down to the ends of the hair with every stroke, and check the comb for lice.
  • Remove lice by wiping or rinsing the comb.
  • Work methodically through the hair, section by section, so that the whole head of hair is combed through.
  • Rinse out the conditioner and repeat the combing procedure in the wet hair.

Dry detection combing

  • Straighten and untangle the hair using an ordinary comb.
  • Once the comb moves freely through the hair without dragging, switch to the louse detection comb. Comb the hair from the scalp to the end of the hair, combing each section of hair three to four times before moving on to the next section.
  • Look out for lice as the comb is drawn through the hair. If you see a louse, trap it against the face of the comb with your thumb. This helps to avoid the louse being repelled by static electricity as the comb is removed from the hair.
  • Continue combing the hair, section by section, until the whole head of hair has been combed through.

If you discover head lice in your child's hair, check the rest of your family, and alert close friends and your child's school. There is no need for children with head lice to be kept off school. They will probably have had the infestation for several weeks, so keeping them away from school is unlikely to affect transmission.

If live head lice are found, take appropriate steps to treat them immediately. Treatment should only be carried out after live head lice have been found. Do not treat hair 'just in case'.

Medicated lotion or spray

Medicated lotion or spray is an alternative method for treating head lice. However, no medicated treatment is 100% effective. Your pharmacist will be able to recommend an over-the-counter lotion or spray.

Medicated treatments should only be used if a living (moving) head louse is found. Crème rinses and shampoos are not thought to be effective and are therefore not recommended.

Make sure that you have enough lotion to treat everyone in your family who is affected by head lice. Use enough to coat the scalp and the length of the hair during each application.

Follow the instructions that come with the medicated lotion or spray when applying it. Depending on the product you are using, the length of time that it needs to be left on the head can vary from 10 minutes to 8 hours.

The normal advice is to treat once, then repeat after seven days. Some medicated products also supply a comb for removing dead lice and eggs.

Traditional insecticides must not be used more than once a week for three weeks in a row. Some products carry a fire warning.

Some medicated products may be capable of killing eggs as well as lice, although there is no certainty of this. Check for baby lice hatching from eggs three to five days after you use a product, and again 10 to12 days afterwards.

A minimum of two applications of lotion are needed to kill the lice over the hatching period because the lotions do not always kill louse eggs.

If the lice appear to be unaffected by the product (some lice may have developed resistance to a particular insecticide) or if the problem persists, seek advice from your school nurse, health visitor, pharmacist or GP.

Cautions

Always seek advice from a healthcare professional before using medicated head lice lotions on the following groups:

  • young babies (under six months old)
  • pregnant women
  • people with asthma or allergies

Always read the instructions carefully before using medicated head lice lotions.

Head lice and clothing

There is no need to wash or fumigate clothing or bedding that comes into contact with head lice. Head lice can only survive on humans and they die after a day or two of being away from the human scalp.

Preventing

A head lice infestation cannot be easily prevented. Regular detection combing - for example, on a weekly basis, is the best way to find new lice quickly.

Medicated lotions and sprays are not effective in preventing head lice infestations. They should only be used if a live louse has been found on your or your child's head.

Source: HSE Ireland & NHS Choices websites