Hormonal changes. Stretch marks develop in times of increased glucocorticoid production, for example during puberty, pregnancy, with Cushing's syndrome or with external steroid use. High steroid hormone levels have a catabolic effect on the activity of fibroblasts and decrease the deposition of collagen in the ground substance of the dermal matrix. Clinical publications confirm that hormonal changes are one of the main reasons for stretch mark development. It is a defect in the basic structure of the elastic tissue. This theory was posted after a relationship was found between stretch marks and increased vaginal lacerations at birth. An extracellular matrix defect may also explain why overstretched tissue leads to ruptured collagen fibers and hence stretch marks in some individuals who experience rapid weight change e.g. during pregnancy or when suffering from Cushing’s syndrome. Mechanical stretching can lead to the rupture of the connective tissue framework during pregnancy, growth spurts in adolescence, obesity and rapid increase or decrease in weight.