Worms are parasites which can infect the intestinal tract of humans. Most commonly it is threadworm, also known as pinworm, that will be encountered particularly in young children. The worms are up to 13mm in length and look like cotton thread in their stools. They are caught by unknowingly eating the eggs of the worm by sharing food, toys or books. Simple washing of hands before eating or after using the toilet can reduce the risk of catching the infection. The main symptom is often anal itching, which is worse at night. This can lead to disturbed sleep, tiredness, irritability and loss of appetite. Treatment is a single tablet or dose of medicine when hygiene advice is followed.