First of all, to better understand what are stretch marks we must better understand what the skin is.

Collagen and elastin create and form a connected "skin network". elastin is a protein, and we must clearly understand that it allows the skin to have stretching properties. The presence of a stretch mark implies the damage of the elastin.

Scars are what replace normal skin after an "injury"(any type of damage to the skin). They are quickly created by the body to reconnect collagen and elastin skin fibres. The skin can't take too much stretching, and up to a certain point it is torn, this is the case of stretch marks. The appearance of a stretch mark on the skin, implies the degeneration of the skin network and its components in between the outermost and second layer of your skin. A stretch mark is a scar that, even though it may seem as if it were ON your skin, is actually found UNDERNEATH it, in other words a stretch mark is a linear artophic lesion.

Now we must understand what's happening at the area of the elastin fibres and collagen network. Bundles of protein, also known as elastin fibers are found in the connective tissue. Elastin fibers can be pulled to grow up to 1.5 times their size and then once untensed can move back to the original size. But it can occur that once the stretched skin, molds back into place, it can leave behind a stretch mark.

The Formation of Stretch Marks

Basically what stretch marks are is damaged tissue, this is what makes the fibrocytes react and put into movement a process of mitosis of the fibrocytes.

Once this process takes place, the stretch marks could incline themselves to the result of a persistent stretch mark process after they have appeared. But the "stretching of the skin", is not the only association one can make to stretch marks. "Stretch marks" may come to be for many different factors.

* Mechanical factors linked to skin's fragility: This means weight increase, pregnancy, growth. Endocrine factors due to malfunction of the pituitary-hypothalamic complex. This means that there is a disregulation of cortisol (hypercortisolemia) that triggers the degradation of the collagen network.

* Clinical factors: local or systemic treatments with corticoids.

* Metabolic factors: such as glycation or sugar metabolism disorders which inhibit the biosynthesis activity of fibroblasts and non-enzymatic glycosylation, the Maillard reaction, leading to cross-links in proteins such as in collagen between the amino-acids arginine and lysine that reduces skin's elasticity.

It is evident that stretch marks don't only come from weight gain and rapid growth, but also come from clinically induced and hormonal situations. Stretch marks radicate from many sources, but the consequence is undeniable; an uncolored, stretched line that ends up being as stubborn as any other scar and impossible to remove no matter what stretch marks removal you use.