Stretch marks (striae distensae) are a common form of linear skin scarring resulting from the rapid expansion or contraction of the skin. They occur when the skin’s underlying support structure cannot keep pace with sudden changes in body size. While this phenomenon affects all genders, prevalence is significantly higher among women, particularly during certain periods of life.
Global Prevalence: Answering the “How Many” Question
Stretch marks are an extremely common dermatological finding, with research suggesting that overall prevalence in the general female population ranges widely from 11% to 88%, depending on the specific study and population surveyed. The incidence is especially concentrated around periods of rapid physical change, which are naturally more frequent for women.
The highest rates are consistently seen during pregnancy, with estimates showing that 50% to 90% of pregnant women develop the marks, often referred to as striae gravidarum. These commonly appear on the abdomen, breasts, and thighs, usually beginning in the second and third trimesters as the body expands to accommodate the growing fetus. Puberty also represents a high-risk period, with up to 70% of adolescent girls developing stretch marks due to rapid growth spurts and hormonal shifts associated with maturation.
The Biological Mechanisms and Triggers
Stretch marks form when the dermis, the middle layer of skin, is subjected to stress that exceeds its capacity to stretch. This stress causes microscopic tears in the dermal connective tissue, leading to the disruption and reorganization of the essential protein fibers, collagen and elastin. While the outer layer of skin, the epidermis, remains intact, the damage to the underlying dermis results in the visible scarring.
The most common mechanical triggers are rapid weight gain, sudden weight loss, or the intense growth spurts experienced during adolescence. Pregnancy combines this mechanical stretching with significant hormonal changes, which further contributes to the skin’s susceptibility to tearing. Elevated levels of glucocorticoid hormones, such as cortisol, weaken the skin by inhibiting the function of fibroblasts, the cells responsible for producing new collagen and elastin fibers.
Hormonal influence is a key factor, as physiological events like pregnancy and puberty involve substantial shifts that can impair the skin’s regenerative capacity. When fibroblast activity is reduced, the skin’s structural matrix is less able to repair itself and withstand the mechanical tension from rapid expansion. Genetic predisposition also plays a role, suggesting that some individuals are born with a skin structure inherently more vulnerable to this type of scarring.
Approaches to Appearance and Fading
Stretch marks progress through two main stages: the initial inflammatory phase and the later chronic phase. The first stage is known as striae rubrae, characterized by a red, pink, or purple color due to the presence of dilated blood vessels and inflammation in the dermis. These newer marks are slightly raised and are the most receptive to treatment because of their active blood supply and ongoing biological processes.
Over time, the marks mature and enter the second stage, called striae albae, where they become white or silvery and appear slightly depressed and atrophic, resembling old scars. This color change occurs because the blood vessels constrict and the inflammatory cells dissipate, leaving behind a permanent alteration in the skin’s structure. At this stage, the skin shows a loss of elastin and a parallel arrangement of collagen fibers, which is typical of scar tissue.
For marks in the striae rubrae stage, topical treatments that stimulate collagen production are often suggested. Derivatives of Vitamin A, such as topical retinoids like tretinoin, can improve the appearance of newer marks by promoting fibroblast activity, though these must be avoided during pregnancy and breastfeeding due to safety concerns. Other topical options, including those with hyaluronic acid or Centella asiatica extract, are used for intensive moisturization and to support the skin’s barrier function, although evidence for total elimination remains limited.
Once the marks have become white (striae albae), topical treatments are significantly less effective, and professional interventions are pursued for improvement. Medical procedures are designed to remodel the scarred tissue and include treatments like fractional laser therapy, which creates micro-injuries to stimulate new collagen and elastin synthesis. Other techniques, such as microdermabrasion and chemical peels, aim to improve skin texture and stimulate dermal repair. Stretch marks are permanent scars that fade naturally over many years.