Many young children pick their butts. Sometimes, kids pick their butts because they feel like exploring the wonders of the human body in public and have no regard for social norms. Sometimes they do it because they haven’t wiped properly, and there’s something worth picking. But, more often than you would think, kids pick their butts because they have intestinal parasites living in their colons. “Pinworms are a reason why kids might pick their butts,” says pediatrician Mildred F. Carson, M.D.

Pinworms are a distinct possibility — the intestinal parasite infects up to half of children between the ages of 5 and 10, and it is the most common parasitic infection in the U.S., according to the Centers for Disease Control and Prevention.

The white and narrow worms are incredibly contagious and can be passed through accidentally inhaling or ingesting the eggs. Once in a child’s body, the pinworm eggs stay in the intestines until they hatch and grow to full size (about half of an inch). From there, female pinworms travel through the body to lay eggs around the anus, before heading back into the colon. Those itchy eggs are why many kids pick at their butts.

Of course, parasites are not the only reason children are prone to butt-picking. “Children that are not wiping or being wiped thoroughly can have stool left behind and this will cause extreme itching,” Carson notes, adding that pieces of toilet paper can get caught behind and add to irritation and itchiness.

Allergic reactions and sensitivities to certain laundry detergents can also cause itching and irritation. “I recommend parents wash all their kids’ clothing prior to use to decrease the possibility of reactions to dyes and chemicals,” Carson says.

A pediatrician can test for pinworm eggs with a simple tape test and treat it with oral medications. Throw in a quick refresher course in wiping, and you should be able to solve any remaining problems.

If, even then, you find your kids picking their butts, consider the remaining possibilities. “Parents should also check the size of their child’s underwear to make sure the size is correct because this can make children pick at their bottoms,” Carson says.

This article was originally published on Aug. 21, 2018