what causes stretch marks?

I wanted to know how you get stretch marks because when people get them some stay some don’t do I want to know what causes them

Stretch mark is caused by a stretching of the skin, coupled with an increase in cortisone level(hormone produced by the adrenal glands) Cortisone may weaken elastic fibers in the skin.
Stretch marks develop in a variety of condition such as pregnancy, weight gain, sometime chronic use of oral or systemic steroids, cushing syndrome and adrenal gland diseases can also cause stretch marks.