As we work from top to bottom, let's look at the problem of head lice.

The head louse, also known as Pediculus capitis, is a small dark parasitic insect of about 3mm in length. It needs the moisture and warmth found on the scalp to survive - hence making this its home - and has a predilection for the nape and behind the ears. It feeds by piercing the skin of the scalp and sucking blood from the host. After mating, the female louse lays about six to eight eggs a day for the rest of her short thirty-day life. These eggs are creamy white and are stuck to the hair shafts. After about seven to ten days, the eggs hatch and leave behind empty egg shells known as "nits" (see the picture below to see what a nit looks like). It takes a further 6-14 days for the newborn lice - known as "nymphs" - to mature to adulthood and restart the reproductive process.

A normal infestation involves ten to thirty lice, but the range is wide. Head lice stay on the head and do not migrate to other parts of the body. They are not carriers of disease and do not cause many adverse effects - the biggest complications are itching (usually due to the injection of louse saliva under the skin while feeding, or the deposition of louse faeces onto the scalp's skin), as well as embarrassment and anxiety. Very occasionally the scalp can get infected because of excessive itching and scratching, but again this is rare.

Head lice are very common amongst primary school aged children between the ages of 4 and 11. The lice cannot leap or fly, but can crawl relatively fast - transmission is therefore due to head to head contact amongst children. It is the adult louse who will cause the infection, as the nymphs cannot spread. Some say that sharing things such as helmets and towels increases the risk of transmitting head louse infection - although theoretically the louse can survive away from it's host for up to two days, it probably does not last very long once it has left the scalp.

The only true way to confirm an infestation is to see one live crawling louse. Even if the child has clearly visible eggs or nits, unless a live moving louse is seen an active infestation cannot be confirmed. The way to do this is through "structured detection combing" using a very fine toothed comb, with teeth spaced less than 3mm apart. This technique has proven to be more effective than direct inspection. This is very important, as you should not start treatment for head lice unless you have actually seen a live louse.

Treatment involves three different approaches: use an insecticide such as Aqueous Malathion 0.5% Lotion or Phenothrin 0.5% Liquid, Dimeticone 4% Lotion or using wet combing with the afore mentioned fine toothed comb (a normal comb will not work).

Wet combing (recommended over dry combing) is done by washing hair as normal, applying conditioner and detangling with a normal comb. Following this switch to the fine toothed comb and working the comb from the scalp to the tip of the hair, working your way systematically around the whole head. This needs to be done four times over the space of two weeks

Using the insecticides, apply the lotions to dry hair making sure it is all covered from root to tip. Let it dry naturally and leave it on for 8-12 hours (or overnight). Following this wash the hair as normal and repeat the procedure a week later. After two or three days perform the detection combing with the fine toothed comb. If there are no lice or nymphs, repeat the combing 10 days later, if there is still nothing then treatment has been successful. If there are nymphs or lice then treatment has been unsuccessful, but if there are only adult lice then your child may have been infected afresh. Re-treatment needs to be applied.

No one treatment is 100% effective as sometimes the lice are resistant to the products, sometimes the product is not applied in large enough quantities or correctly - but this shouldn't stop you from going for it and zapping those little critters!