They represent linear dermal scars accompanied by epidermal atrophy. Skin distension apparently leads to excessive mast cell degranulation with subsequent damage of collagen and elastin. Genetic factors could certainly play a role, although this is not fully understood.
Stretch marks affect all races.
Striae affect women more commonly than men. Early striae present as flattened, thinned skin with a pink hue that may occasionally be pruritic. Their surface may be finely wrinkled. Mature striae assume white, depressed, irregularly shaped bands with their long axis parallel to the lines of skin tension. They are generally several centimeters long and 1-10 millimeters wide.