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Threadworms (pinworms)

4-minute read

What are threadworms?

Threadworms, also called pinworms, are tiny parasites that grow to about 13mm in length and look like tiny pieces of white thread. They live in the intestines.

How does threadworm infection occur?

People, usually children, get infected with threadworms by getting threadworm eggs on their hands and then putting their hands in their mouths. They swallow the eggs, which travel to the lower intestine where they grow into worms. The worms then move to the anus to lay their eggs. (The anus is where stools (poo) leave the body.)

The worms usually lay their eggs at night and both worms and eggs make the anal area itchy. If the skin around the anus is scratched and the hands are not carefully washed, the eggs on the hands can get back into the mouth, repeating the cycle.

Threadworm eggs are usually passed from one person to another. Worms can live on the skin, toys, and other objects for several weeks. If you touch your mouth with your hands after touching a contaminated toy or other object, you can become infected.

Humans do not catch threadworms from animals.

What are the symptoms of threadworm infection?

The main symptom is itching in the anal area. A child may have trouble sleeping because of the itchiness. Girls can also have redness and itching around the vagina.

How is the infection diagnosed?

It may be possible to see the worms on the person’s underwear. They may also be seen at night around a child's buttocks. A doctor may suggest treatment for threadworms even if the child only has an itchy bottom since the infection is both common and easy to treat.

How is it treated?

Threadworms are easily treated with medicine prescribed by a doctor or available from your pharmacist. Usually the medicine is taken as a single dose, which is then repeated 2 weeks later. It is recommended that the child showers on the night the medicine is given and again the next morning to remove eggs laid during the night.

It is also very important for the whole family to be treated at the same time, which is sometimes referred to as ‘worming the family’. It is very easy for the whole family to become infected because the eggs are easily passed from one person to another within a household, from hands or fingernails to towels, sheets and other surfaces.

When treatment is started, it’s important to wash sheets, towels, clothes, and anything else that might have eggs or worms on it, such as toys, in hot water. Also, make sure everyone changes their underwear every day. Be sure that everyone washes their hands before eating and after using the bathroom. Keep fingernails trimmed short.

How do I prevent threadworm infection?

Unfortunately, repeat infection is very common. To help reduce this and to prevent the threadworms from spreading to others, you can take the following precautions:

  • Treat all other family members at the same time. Adults can also get threadworms.
  • It is not necessary to 'worm' the family when you worm the family pets. Dogs and cats do not get threadworms or pass them on to humans.
  • Encourage your child not to scratch, despite the itching.
  • Keep your child's fingernails clean and trimmed. Encourage children from biting their nails or thumb sucking.
  • Have your child wash their hands with warm soapy water for at least 10 seconds after going to the toilet. Ensure they practise good personal hygiene.
  • Launder bedding and toys in hot water.
  • Vacuum often, to remove any eggs. 
  • Discourage your child from eating food that has fallen on the floor.

Should I keep my child home from school?

Here’s a list of common childhood illnesses, including threadworms, and their recommended exclusion periods.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: April 2020

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