|Stretch marks are actually a hereditary condition. They are scars on the skin from stretching. When the body grows faster than the skin has the ability to grow, you will get stretch marks. A lot of people get them. When I was a teenager, I had a friend whose chest grew so fast, she had what looked like giant red scratches all over her breasts. They were stretch marks, but I didn't know it at the time.
While people will say use lotion, baby oil, or cocoa butter - those things will neither prevent or get rid of stretch marks. Stretch marks will lighten over time, turning more into a silvery skin color instead of dark red/purple color. Lotion won't hurt you, however, and if you feel it helps, then by all means you should use it.