Yup, totally normal. It’s unclear exactly why baby boys get erections, but they do, often while you’re changing their diaper. Just chalk it up to biology keeping everything functioning properly down there.

If you notice your baby’s erection goes down quickly and doesn’t seem uncomfortable, then don’t worry about it at all. But if the erection lasts more than an hour, there’s redness or swelling, or he seems uncomfortable, take him to the pediatrician. You’ll want to make sure there aren’t any obstructions of the penis.

Other boy-specific symptoms you’ll want to watch out for are a painful or swollen scrotum; any pain that lasts over 24 hours or is severe; trouble peeing; foreskin that’s red, swollen or looks infected (if he’s not circumcised); a rash that worsens or lasts more than three days; pus or bloody penile discharge; tiny water blisters; sores; or any of those symptoms accompanied by a fever. All of these are worth a trip to baby’s doctor.

Plus, more from The Bump:

10 Weird (But Totally Normal) Things About Newborns

Circumcision Care Basics

Should We Circumsize Baby?

Alanna Levine, MD 's Latest Articles