First let’s take a look at their location.

[Bonnie Carl]

Just like the heart and the lungs and the stomach, the skin is by
definition an organ. Of all of the organs in mammals, the skin is by
far the largest. This is why people with deep, massive burns are often
not expected to live.

http://stretchmarkinstitute.com/6,what-are-stretch-marks.html

[Bonnie Carl]