Stretch Marks

Stretch Marks

Striae distensae are mechanical failures of the dermis. When skin is stretched faster than its connective tissue can remodel, collagen and elastin fibres rupture along lines perpendicular to the direction of tension, and the resulting linear scars sit below an epidermis that remains intact. That is why the marks are flat or slightly indented rather than raised, and why they cannot be exfoliated away: the defect is dermal. They affect 50 to 90 percent of pregnant women and are common through adolescent growth spurts and rapid weight change. One ingredient carries an evidence grade here, collagen peptides at Grade D on 2 studies and 120 participants.

The condition has two stages that are frequently treated as one. Striae rubrae are new, reddish-purple, and inflamed, with dilated vasculature visible through thin overlying skin. Striae albae are mature, white or silvery, atrophic, and hypopigmented because melanocyte function is reduced within the scar. The distinction matters more than any other fact on this page, because the red stage retains active fibroblasts and residual inflammation while the white stage is settled scar tissue. Interventions of any kind have consistently shown more influence on striae rubrae than on striae albae, and the window between them is measured in months.

Mechanical stretch alone does not account for the distribution. Corticosteroid exposure, whether endogenous as in Cushing syndrome or exogenous, produces striae independently of rapid growth by suppressing fibroblast collagen synthesis, which is why the marks appear in patients on systemic steroids without weight change. Pregnancy combines both routes, mechanical stretch of the abdomen with the hormonal shifts of gestation. Family history is among the strongest single predictors, pointing at inherited differences in dermal elastic architecture.

Collagen peptides are the sole graded entry and the rating reflects the state of the evidence rather than the plausibility of the idea. Two studies and 120 participants cannot distinguish a real effect from the natural course of the condition, which is itself a substantial confounder: striae rubrae fade toward striae albae without any intervention, so an uncontrolled trial reading improvement over three months is describing maturation. The mechanistic argument, that supporting dermal matrix synthesis during a period of rapid stretch might reduce the extent of fibre rupture, is coherent and untested at scale.

Two practical observations follow. Timing dominates, since the biology suggests any influence would be greatest during formation and early in the red stage, and almost no trial is designed to catch that window. And the strongest evidence in this area concerns interventions applied topically to the developing striae rather than anything taken orally. Striae that appear without pregnancy, growth or weight change, especially if wide and purple, warrant evaluation for cortisol excess.