Stretch marks appear as parallel strips of lines, separated by stretches of healthy skin; to start with, stretch marks are a red-purple colour due to the thinness of the epidermis which shows the venous network. The stretch marks then “heal” turning a pearly white colour and appear as slight furrows on the skin or sometimes they are even slightly raised, just like a scar. They usually appear on the thighs, hips, buttocks, abdomen and breasts.

These lesions can occur at any age, although for the most part they are found in women of between 15 and 30 years of age, who are affected twice as often as men, and in particular during pregnancy and puberty. They are usually grouped in twos or threes, parallel to each other and perpendicular to the direction in which the tensile forces act on the skin. The onset is usually asymptomatic, but they can be accompanied by a slight itchy feeling or, more rarely, by a burning and painful sensation. The colour depends on their stage of development: at the beginning when the inflammatory, pseudohypertrophic, component prevails, it varies from pink to red to purple or bluish red while, later on in the scarring phase, they are thinner, pleated, depressed to the touch and become a pearly white colour.

Women are affected twice as often as men. One of the major causes of this imperfection is the lack of elasticity of the dermis. The probability of the appearance of stretch marks increases if this basic condition is associated with a rapid increase or decrease in weight over a short time: the abrupt skin distension due to sudden increases and decreases in weight can, in fact, cause the collagen fibres to rupture along with a traction of the capillaries of the dermis with consequent damage to the tissues. It is still unclear whether there is a genetic predisposition. The conditions that facilitate the appearance of stretch marks are growth and pregnancy.

The biochemical hormonal factor is also the primus movens during pregnancy too, especially between months 6 and 8 when the glucose tolerance decreases and the concentration of blood ketogenic steroids increases. It can also be affected by more or less intense sporting activities, due to the increase in muscle volume followed by long periods of inactivity. Even a prolonged systemic therapy with high-doses of cortisone or steroids can cause the appearance of stretch marks.

Stretch marks procure permanent skin damage and, in actual fact, they are scars.

From a histological point of view the atrophic mark corresponds to a thinning of the epidermis combined with the atrophy of the skin’s collagen bundles, associated with a decrease in elastic fibres around the edges of the stretch mark which appear retracted and thin; this area of ​​atrophy is not vascularised.

Pathogenesis: there are three different phases of the formation of stretch marks:

  1. a) the preclinical phase: interruption of the function of the fibroblasts and a physical chemical modification of the basic substance (less mucopolysaccharides and decreased activity of glycolytic enzymes) with consequent alteration of the collagen and elastic fibres.
  2. b) regenerative phase: recovery of the enzyme activity (increased oxidoreductase, acid and alkaline phosphatase and non-specific esterases), activation of fibroblasts, increased mast cells, restoring the production of mucopolysaccharides. This corresponds clinically to what are referred to as striae rubrae.
  3. c) healing phase: the enzymatic activity of the fibroblasts returns to normal, the collagen fibres followed by the elastic fibre, are regenerated and restore the damaged connective tissue with an appearance observed using a microscope similar to that of scar tissue (striae alba).