What causes stretch marks?

[bbmccorm]

I've had stretch marks on the inside of my thighs for many years that show more prominently at some times than others. I've never gained or lost a lot of weight in my life, and they tend to be fairly noticeable at some times and almost completely unnoticeable at others so I'm curious what causes this. Any insights?

 

[Charger]

I'd be interested in a Peaty solution for removing them, but I doubt there's anything effective.

I'm guessing high estrogen and cortisol makes you more prone to develop them.