When she was in her 30s, Donna Hayes made an unusual career jump: from opera singer to podiatrist. Why the change? She wanted to do something more service-oriented, and she had noticed that the doctor who performed her mother’s bunion surgery “seemed to have a real good life.”

After four years of medical school and three years of residency, Donna achieved her second dream. She now works as a traveling podiatrist with Aggeus Healthcare and primarily services patients in nursing homes—so she’s familiar with how a lifetime of use affects our feet. We sat down with her to double-check some popular claims about foot health and the shoes we choose.

Claim: Heels are terrible for your feet.

Her Verdict: It depends on the heel and the feet.

If Dr. Hayes could ban one shoe from the world, it would be the high stiletto heel. “That’s just a dangerous shoe,” she said, citing risks from toe cramps and blisters to stress fractures and sprained ankles. When you wear high heels, “you’ve totally shifted onto your foot [and] increased the stress by 7 to 10 times what it would normally be.” Habitual heel wearers can even displace the pad on the balls of their feet, resulting in a pain known as metatarsalgia.

But not all heels are bad. If you’re going to dress your feet up, Dr. Hayes recommends heels between 1 and 2 inches high. In fact, if you have “a naturally tight heel cord [or] if you’re a toe-walker anyway, … a little heel is good.”

Dr. Hayes admits she still wears “unhealthy” heels occasionally. “We’re social beings. We want to fit in and we want to be sexy.” So it’s all about moderation. (See more advice for wearing and walking in heels.)

Claim: Flip-flops will ruin your arches.

Her Verdict: True, if they don’t support your feet the right way.

Wearing flat flip-flops stretches out the plantar fascia, the thick connective tissue that runs on the bottom of your foot from your heel bone to your toes. “I think of the [plantar fascia] as a rubber band. There’s some elasticity there, but if you stretch a rubber band to its end point for a long period of time, eventually you get little fractures.” Traipsing around in unsupportive flip-flops causes micro-tears in the tissue, and those tears are responsible for the heel pain that Dr. Hayes called “the common cold of the foot”: plantar fasciitis.

Some flip-flops, however, do have arches built in—Birkenstocks, for example. Still, getting the right type of arch support is tricky. Dr. Hayes has extremely flat feet, so Birkenstocks would overcorrect for her lack of arch support, and she’d get a blister in her arch. She tries to buy flip-flops that have a more gentle slope to them.

Claim: If the shoe fits, wear it.

Her Verdict: It’s a little more complicated than that.

When checking for fit, many people don’t realize width is as important as length. Donna said shoes with a triangular top can be especially constrictive. See if you can spread your toes out while wearing them—otherwise, you might be compressing the nerve that goes between your third and fourth metatarsal bones, which can lead to a burning pain called Morton’s neuroma.

But even a shoe that fits well can still be wrong for your foot. Once you’ve found a pair you like, put it to two tests: “Twist the shoe back and forth [along its length]. A lot of twisting isn’t a good thing. You also want to make sure that it bends right where your toes bend, at the joint.” Dr. Hayes mentioned Asics and New Balance as brands that tend to pass these inspections.

Claim: If nothing’s wrong with your foot, you don’t need to see a podiatrist.

Her Verdict: It can’t hurt, and it might help!

Dr. Hayes said a trip to the podiatrist can identify the nuances of your foot’s shape. That way, “you have an understanding of what kind of shoe you’ll need for the rest of your life.” You’re not likely to find a laser that can measure your arches anywhere else.

She also mentioned specialized running-shoe stores, where the staff will examine your feet and direct you to shoes that match your profile. As someone who’s “extremely pronated,” Dr. Hayes thinks highly of this service. “If you’re athletic, I would definitely go and have them analyze your feet. No question.” (Learn more about how the process works.)

Claim: Feet are gross. Podiatry is a gross profession.

Her Verdict: “Well, it’s better than being a proctologist.”

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Photos by Andrew Nawrocki, Groupon