Pinworms are usually caused by swallowing tiny pinworm eggs, most often through contaminated hands, food, bedding, or surfaces. The eggs hatch in the intestines, and the cycle can continue when scratching spreads eggs back to the mouth or to other people.

How it spreads

  • Touching contaminated items and then putting your fingers in your mouth.
  • Sharing bedding, towels, clothing, or other objects that have eggs on them.
  • Poor hand hygiene, especially after using the bathroom or before eating.

Why it keeps coming back

Female pinworms lay eggs around the anus at night, which can cause itching; scratching can move eggs onto the fingers and under the nails, making reinfection easy. This is why pinworms often spread within households and among school-age children.

Simple prevention

  • Wash hands well and often, especially after bathroom use and before eating.
  • Keep nails short and avoid nail-biting or scratching.
  • Wash bedding, pajamas, and underwear regularly.

If you want, I can also give you the usual treatment and how to stop reinfection at home.