You may have heard the rumors—they sound like something your grandmother would say: “Don’t wear those flippity-flop thingies; they’re bad for your feet.”

Well, it’s more than an old wives’ tale; according to the American Podiatric Medical Association (APMA), the majority of flip-flops aren’t good for your feet for long periods of time.

I know what you’re saying—they’re cool, they’re comfortable. How could something that feels good on your feet be “bad” for them? The problems are many-fold, unfortunately.

Chances are you don’t even notice that your foot has to work in order to keep most flip-flops in place. In a recent report in USA Today, experts say that keeping a flip-flop on works muscles in your shins unnaturally and shortens your stride, straining your lower legs. This hurts your knees, hips, and back. And this is far from the first study to find this, just one of the latest.

Shoes that conform to your foot are better, lead researcher Justin Shroyer, an assistant professor of kinesiology at the University of Louisiana-Lafayette, says in the article. According to him, you should look for flip-flops with heel cups and arch support. Big straps are better, and back straps help.

The other problem with flip-flops is shock absorption. But aren’t most flip-flops nicely padded? Despite what you may think, they’re not sufficiently able to absorb shock like they should be, research shows—and the more weight on them, the worse the problem.

So should flip-flops be off your summer list, cool and comfortable or not? Not necessarily. Not all flip-flops are created equal, and yes, you get what you pay for. Generally, the cheaper flip-flops are the trouble-makers, whereas brands like Birkenstock, Born, Clarks, Crocs, and Teva are on the “ok” list. The APMA has gone so far as to give a stamp of approval for certain flip-flops, so offerings from Chaco, Dansko, and SOLE among others are even better.

Here are some Do’s and Don’ts for flip-flops:

– Buy flip-flops of high-quality leather to help prevent chaffing.
– Look for flip-flops with the APMA’s seal of approval–they’re looking out for your foot’s well being.
– Bend the flip-flops from end to end; look for flexibility, but they shouldn’t fold in half.
– Make sure your flip-flops are big enough your foot doesn’t hang over.

– Keep wearing worn-out flip-flops.
– Wear flip-flops that cause blisters
– Walk long distances in them—they’re best for around the pool
– Work in the yard wearing flip-flops
– Play sports in flip-flops

The upshot is that flip-flops have their place, and they can be cute, cool, and comfortable…but all things have their place. So keep your thongs at the pool or beach, where they belong, and get a proper sport sandal for everything else.