Nelie -- I thought the same thing as Karen.

I used to get all sorts of red streaks all over my shoulders from hack squats and the standing calf raise machine. They'd last 3 - 4 days and then fade. I don't get them at all any more, though -- perhaps my shoulders have petrified and turned to rock or something?
If they are brand new stretch marks that are still red and they bother you, talk to a dermatologist. I was told by mine that this is the ONLY time that they can be treated -- while they're new and red. And the only effective thing is prescription only.