Threadworms are a common problem in childhood. Approximately 50% of children will have threadworms at some time during their lives, and sometimes adults are affected too. The most common symptom is an itchy bottom at night, but you may sometimes see silk-like threads in your child's stools. The worm spreads because children scratch their bottoms at night when the worms lay their eggs on the skin. The eggs are then transferred to the mouth.

Usually it is possible to clear the infection by a single dose of medicine (mebendazole) that you can buy from the chemist or obtain on prescription. There is enough medicine in the bottle to treat six people and it is usually wise to treat the whole family as the worms spread easily. The medicine should not be taken by children under two or pregnant women. You may have to repeat the medicine two weeks later if the symptoms have not settled.

As well as using the medicine make sure that finger nails are clipped short, hands are scrubbed before meals and the children wear underpants and pyjamas at night. This will make it difficult for the worms to spread. It is possible to eliminate the infection this way and, of course, this can be done in pregnancy when the medicine is not safe to take.