First let’s take a look at their location.

[Robert Appel]

Stretch Mark.
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. A bodily organ is a collection of tissues that
are structurally joined for a purpose. The skin is a marvelous model
of indispensable function.
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