What will happen if you don't treat pinworm?

Itching: especially at night, will continue. They can migrate into the vagina and urethra laying eggs there and leading to itching in one or both locations. See this video https://www.youtube.com/watch?v=PrUlhufWlIA

Annoying symptoms: Pinworm infestation causes the annoying symptoms of rectal itching, usually at night, and if not treated, one keeps reinfecting oneself by scratching and ingesting the eggs that were deposited when the worms come out at night to lay eggs. An uncommon complication happens if the worms get stuck in the appendix, leading to acute appendicitis that would need surgery to remove the appendix.