We must look into the skin to really understand what stretch marks are.

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. Damaged elastin shows itself on the skin as a stretch mark.

Posterior to an "injury"(any type of damage to the skin) normal skin is replaced by a scar. To quickly connect collagen and elastin fibers, the body leaves us with stretch marks. The skin can't take too much stretching, and up to a certain point it is torn, this is the case of stretch marks. A stretch mark is a result of a weakening of the "skin network", which includes the cells and the connective fibre tissues in between the first and second later of skin. A stretch mark is a scar that is not actually on the surface of your skin, but in between your first and second layer of skin.

it doesn't just end here, we also have to look into the elastin fibers and the collagen network. Bundles of protein, also known as elastin fibers are found in the connective tissue. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed. But it can occur that once the stretched skin, molds back into place, it can leave behind a stretch mark.

How Stretch Marks are Formed

In reality a stretch mark is really damaged tissue, once tissue is damaged fibrocytes begin to undergo a process of mitosis.

This process of mitosis may leave you with a group of stretch marks instead of just one. We must keep in mind though that the stretching of the skin is not necessarily the only reason one may have a stretch mark. There are actually four factors that can cause the dreaded deep "stretch marks".

* 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 important to keep in mind that stretch mark do not only appear because of weight and growth reasons, they appear for hormonal and external reasons also. The ways you can get a stretch mark are many yet, but the outcome is the same; a pale, elongated line under your skin, that shows itself immune to most stretch marks removal.