Danger ranking: 5+. "The flattest, flimsiest styles of these shoes can do as much harm—if not more—than a pair of high heels. Overwearing flats can cause pain in the arches, bunions and the heels. There's absolutely no cushion or support, but people wear them like they're athletic sneakers. That's what makes them dangerous."
Best for: Dining alfresco; watching a play at an outdoor theater
Avoid: Museum tours; hopscotch
Doctor's note: "Commute in running sneakers and then change into these at your destination."