Pinworms are caused by a tiny, harmless worm called Enterobius. It's about the size of a staple. The way you get it is you ingest an egg not knowing it. They're microscopic. And the eggs mature inside into a worm. The worm lives inside your body. You don't feel a thing. The problem is when the adult female egg comes out to lay her eggs, usually at night. She comes out the same way your poop comes out, out of the rectum, she lays the eggs there, and that can cause extreme itching. So some people even lose sleep from this itching but don't even know why they're scratching. Then the next morning, they touch things - bathroom fixtures, or cups and spoons - and they spread the infection to other people. The way this is treated, if your doctor suspects it, is with a simple anti-worm medication. One of them could be called mebendazole. You take it once. and then you may repeat it a week later. The other thing is to really try to limit the spread to other people. So you want to try to keep the affected person's nails very short. Wash their hands first thing when they get up in the morning. And clean underneath their nails. And make sure you wash all your bed linens.