Many breast pumps come with a nipple flange, and it's easy to assume that the one your pump came with is the one you're supposed to use. However, you may need to size up or down to fit your unique breast and nipple shape properly.

A nipple flange is the part of your breast pump that creates a seal around the nipple and areola, allowing for efficient milk extraction during pumping. It helps create a vacuum that mimics a baby's natural sucking motion and facilitates breast milk transfer into the pump's collection container.

Signs of a poor-fitting nipple flange: If you're experiencing pain, redness, milk blebs, or struggling with suction and milk output, it could be related to the nipple flange.

We love this visual guide from Dr. Brown's Baby site to help you distinguish between too small, too big, and just right:

If you think you're in the wrong size, you'll want to take some measurements. BeauGen has made a measuring "roller" that is allegedly more gentle on sore nipples than a ruler. You can print and download it in the comfort of your home.