I used to have stretch marks on my thighs but now you can still see them but they're white what is happening ?

Technically...: ...you still have stretch marks. Initially they are reddish but they get lighter with time. They can occur any time you are growing rapidly and often appear on the breasts, thighs & buttocks of girls as they go through puberty. As long as you maintain a healthy weight, they won't get worse and they are harmless. Hope this is reassuring. Dr. Anne.