I too have generally always worn flat shoes, so I think my bunions have come from my knock knees, which naturally make my feet turn outwards and make me bend forward as I walk.
I've had the bunion on my right foot for years and it's very deformed, but in the last three years the left foot is becoming just as bad.
Strangely, I've never had much pain in the right one, but the left one is beginning to bother me, which prompted the gel purchase - when I bought them, they came as a pair, so that's how I've used them.