What could cause pinworms?

Ingesting the eggs. Pin worm eggs are found in the bedding of affected infants & toddlers, shed into their clothing from the skin around their anus where the adult worm lays them. The eggs are laid in a glue like substance that irritates the skin, so the kids are often scratching the area & dispersing the eggs.If the kid or others touch their mouth with contaminated fingers, they get a dose of eggs & start over.