Scratching on the skin is one of the things that can cause stretch marks. Although other things can cause your skin to break and stretch, scratching the skin most definitely amplifies it. This is when pregnant women complain of itching on their bellies and they scratch it, they get stretch marks.
Stretching of the skin depends on its strength and elasticity. So if you scratch and your skin isn't strong and elastic enough, it could break. Stretch mark can also be caused by rapid stretching or shrinking of the skin due to weight gain and weight loss.
To prevent stretch marks, it is best to stay hydrated always. Eat healthy and always add proteins and lots of fruits to your diet. You should also exercise regularly. It helps the skin and elasticity.