A scar is formed when the process of healing is interrupted by some of the factors which contribute to wrong remodeling of the discontinued skin. In some scars a proliferation of collagen occurs, so they get elevated and accented, in some yet a deficit of collagen occurs and they get indented.
Scars can be thin as well, level with the skin and pale in color. Such scars have had normal healing conditions, just enough water, just enough collagen, they are placed in areas where there was no tension forces pulling on the skin.
Whenever the skin is cut deeper than a certain border (basement membrane), it will always be visible in the form of a scar. So whether a mark on the skin will be left depends on the depth of the cut, don’t ever believe that cutting a skin can heal without a scar, it can only be minimally visible.
What kinds of scars are there?
Natural scar: Usually a linear scar level with the skin. Initially it’s always pinkish, and as time progresses it gradually fades.
Hypertrophic scar: Firm, elevated and pinkish scar which remains in the initial area of the wound, and can fade with time.
Atrophic scar: An indentation on the skin that can result from skin conditions or acne.
Keloidal scar: Firm, elevated and red to purple scar which expands out of the initial area of the wound, and expands over time.