One of the most irritating problems for parents as the new school year kicks off is the appearance of head lice in their offspring.

The main difficulty with a condition such as head lice is that, in most cases, by the time a parent notices their child has an infestation, it is already well established.

The most common sign is itchiness and irritation but it takes at least three months for an initial infestation to get to that stage.

Anybody can get head lice but they are much rarer in adults. Infection is common during school holidays as well as during term time.

Parents worry about lice when children go back to school because they think the lice are being caught there.

But many infections are caught from family and friends in the home and the community, not from school.

Health experts from South Downs Health NHS Trust say the simple solution is to check your child's hair carefully every week, so lice are found as early as possible.

Ann Garmston, of the Trust's School Clinic in Brighton, says parents of children starting school are given an information pack and a special comb to check for any problems.

She said: "A lot of people say it is when their children go to school they develop the problem but, actually, it can happen at any time.

"The time it takes for the obvious signs to show makes difficult to know exactly when the problem started."

When checking for lice, the first thing to do is wash the hair well and apply conditioner before drying with a towel.

The hair should be damp and not dripping.

The hair should then be combed. Start with the teeth of the comb touching the scalp at the top of the head.

Draw the comb carefully towards the edge of the hair.

Look carefully at the teeth of the comb in good light and repeat, from the top of the head to the edge of the hair in all directions, working round the head.

Do this for several minutes it takes 10 to 15 minutes to do it properly for each head.

If there are head lice, you will find one or more on the teeth of the comb.

Head lice are little insects with moving legs. They are often not much bigger than a pin head but they can also be as big as a sesame seed.

They live on, or close to, the scalp and don't wander far down the hair shafts for very long.

They can only live on human beings and cannot be caught from animals.

Treatment need not be given unless a person is sure they have found a living, moving louse. Detection combs can be bought from the chemist along with chemical lotions to get rid of the lice.

Mrs Garmston says recent research shows this is the most effective treatment for lice and better than just shampoo or simply combing.

If lice are discovered, it is vital all the people in the home are checked. Regular use of the lotion should ensure the lice are removed after two weeks but it can take longer.

If they persist, parents should see their GP or local chemist for advice.

A popular misconception is that nits are the same thing as lice in fact, they are the egg-cases laid by lice, stuck to hair shafts.

They are smaller than a pin -head and pearly-white in colour. If a person has nits it doesn't always mean they have lice, because when they get rid of the lice the nits stay on the hair until it grows out.

It is often said that headlice prefer clean, short hair but they probably don't much care whether hair is dirty or clean, short or long although short hair may make it easier for them to get from one head to another.

They can't swim, fly, hop or jump: head lice can only walk from one head to another when heads are touching for some time.

You are unlikely to pick up head lice from brief contact with other people.

The longer you have head-to-head contact with someone who has lice, the more likely is you will get them too.

Lewes GP Michael Phillips said: "A lot of parents get upset and embarrassed and think it is some reflection on them.

They might as well get upset because their child has caught a cold.

"As long as it is treated properly and carefully, it can be dealt with simply. It is an extremely common condition and can affect anyone."