What Is a Scar?
Your body slowly begins to dissolve the clot, introducing new cells that will form the basis of your scar. In particular, fibroblasts, a type of cell that stimulates collagen growth, arrive on the scene. Fibroblasts lay down tissue, adding fibers and contracting the scarred area.
Like the tissue that it is replacing, scar tissue stimulated by fibroblasts is made out of collagen. However, the fiber composition of the collagen is different than that of healthy skin. Normal collagen fibers are in a sort of basket weave-style formation. In scar tissue, though, the collagen goes only in a single direction. Thus, it looks different from your normal skin.
scar on arm
Scar tissue is typically inferior to normal tissue in a variety of ways. For example, scars are less resistant to UV radiation than undamaged skin.
This same process can happen in acne-prone skin when zits are popped unsafely, signalling to your body that a wound has occurred. Stretch marks are also a form of scarring caused by tearing the dermis.