Before I had babies, my poor breasts lived in the saddest, cheapest bras I could find. I trusted myself with an armful of random bras in a dressing room, focusing more on how cute they were than how well they fit.

Lots of things changed when I had my first child, including my respect for my undergarments.

As a habitually thrifty person, it’s hard for me to spend, well, any money on anything. I’m all about wearing second-hand stuff that fits OK. But if I can leverage spending versus how much I’m saving, I can justify some quality stuff. One of my favorites? Nice nursing bras.

And it’s not just about wearing something pretty and functional — it’s about breast health.

International Board Certified Lactation Consultant Melissa Morgan says there are three main dangers of wearing an ill-fitting nursing bra: plugged ducts, mastitis, and decreased milk production.

“I see a fair number of women who end up with mastitis from jogging in a sports bra that’s too tight,” she said, or just wearing a tight bra in general.

You might like the look of a tight bra pressing your breasts up and out, but it’s not beneficial for lactation. Anywhere that’s under pressure in your chest region is liable to get clogged milk ducts. That’s when milk gets backed up in the duct, causing nearby tissue to get inflamed and swollen. A blocked duct is usually painful and can lead to mastitis, an infection of breast tissue.

According to La Leche League, “pressure and congestion obstruct lymphatic drainage of the breasts, stagnating the system that rid the breasts of toxins, bacteria, and cast-off cell parts,” which predisposes the breast to mastitis.

If the band of your bra is too tight, it can cause clogged ducts directly under your breasts; a cup that cuts into your breast tissue can cause blockages above your nipples. Even wearing a crossbody purse that’s heavy and digs into your body can cause lactation problems.

Some people are prone to clogged ducts, others are not. It’s always better to err on the side of caution, and making sure your nursing bra or tank top fits you is an easy way to do so.

“It’s worth every penny to have a well fitting bra that’s not going to compress your breast or cut into lymphatic tissue,” Morgan says. “It’s great if you can have a bra that’s been fit by someone who’s trained in doing so.”

And if you’re a mom who’s able to fold her standard bra cup under her breast to nurse her baby, we have not great news: having the pressure of the cup under your bra can create the same problems as an ill-fitting nursing bra, Morgan says.