Stretch marks form when your skin stretches faster than it can rebuild itself, causing the supportive tissue in the deeper layer of skin to tear. They’re one of the most common skin changes humans experience: between 55% and 90% of pregnant women develop them, and up to 86% of adolescents get them during growth spurts. If you have stretch marks, you’re far from alone, and in most cases they reflect completely normal life events like growing, gaining weight, or building muscle.
What Actually Happens Inside Your Skin
Your skin has two main layers. The outer layer (epidermis) is what you see and touch. Beneath it sits a thicker layer called the dermis, packed with collagen and elastin fibers that give skin its strength and bounce. Stretch marks are a dermis problem. When skin expands rapidly, the collagen and elastin fibers can’t keep up. Immune cells in the area release enzymes that break down elastic fibers in the middle of the dermis, and the collagen reorganizes into dense, flat bundles that resemble scar tissue.
This is why stretch marks feel different from the skin around them. The normal texture and architecture of the dermis has been replaced with something structurally simpler. Blood vessels dilate during the early damage phase, which gives new stretch marks their reddish or purplish color. Over time, the blood vessel activity fades, the skin thins further, and the marks settle into pale, slightly indented lines.
The Most Common Causes
Puberty and Growth Spurts
Adolescence is one of the most common times to develop stretch marks, and it happens in healthy, non-obese teenagers simply because their bodies are growing fast. In adolescent males, stretch marks tend to show up on the buttocks, lower back, and knees. In females, they’re more common on the buttocks, thighs, and calves. Interestingly, while stretch marks in general are more common in women, the type that appears during adolescent growth spurts is actually more common in males.
Pregnancy
Stretch marks during pregnancy are so common they have their own medical name. The rapid expansion of the abdomen over several months puts enormous mechanical stress on the skin, and hormonal shifts during pregnancy further weaken the skin’s ability to repair itself. The marks typically appear on the stomach, hips, thighs, and breasts during the second and third trimesters.
Rapid Weight Changes
Gaining or losing a significant amount of weight in a short period can outpace the skin’s ability to remodel. This includes weight gain from overeating, but also rapid muscle growth from intense strength training. Bodybuilders and athletes who bulk up quickly often develop stretch marks on the shoulders, upper arms, and chest, areas where muscle mass increases fastest.
Medications and Hormonal Conditions
Cortisol, a hormone your adrenal glands produce, directly weakens skin structure when levels are chronically elevated. It inhibits the cells responsible for producing collagen, depletes elastin fibers, and breaks down the supportive gel-like substance that holds the dermis together. The elastic fibers near the skin’s surface become fragmented and thin, while deeper fibers collapse into a dense, non-functional network. The result is skin that is thinner, more brittle, and far more prone to tearing.
This is why long-term use of corticosteroid creams, pills, or injections can cause stretch marks even without significant weight change. It’s also why Cushing syndrome, a condition where the body produces too much cortisol, causes distinctive pink or purple stretch marks on the stomach, hips, thighs, breasts, and underarms. These marks tend to be wider and more deeply colored than typical stretch marks, and they can be an early diagnostic clue.
Genetics Play a Bigger Role Than You Think
Some people go through pregnancy or rapid weight gain without a single stretch mark, while others develop them from modest changes. A large genome-wide study identified four genetic regions significantly linked to stretch mark susceptibility. The strongest association was near the gene responsible for producing elastin, the protein that lets skin snap back after being stretched. Variants near genes involved in the skin’s structural scaffolding, including those that produce fibronectin (a protein that binds collagen together), also showed strong links.
Rare connective tissue disorders like Marfan syndrome, caused by mutations in genes encoding the microfiber proteins that support skin and blood vessels, are well known to cause pronounced stretch marks. But the genome-wide findings suggest that even common, subtle variations in these same structural genes influence whether everyday stretch marks appear in otherwise healthy people. If your mother had prominent stretch marks, your odds are higher regardless of what you do.
New Stretch Marks vs. Old Ones
Stretch marks go through two distinct stages that look and behave quite differently. New stretch marks (striae rubrae) are red, pink, or purple. They’re inflamed, with dilated blood vessels and active immune cells in the damaged area. This is the stage where treatment has the best chance of making a difference, because the tissue is still actively remodeling.
Over months to years, stretch marks transition into their mature form (striae albae). The redness fades, the skin flattens and thins, and the marks become pale or silvery white. At this point, the underlying structure looks like a flat scar: tightly packed horizontal collagen bundles, fewer blood vessels, and a thinner outer skin layer. Both stages show similar levels of hydration and elasticity, but they respond very differently to treatment.
What Works for Reducing Their Appearance
No treatment completely erases stretch marks, but several can improve their appearance, especially when started early. Topical retinoid creams, often considered a first-line option, have shown disappointing results in clinical trials. In one year-long study, 80% of patients using topical tretinoin showed only minimal improvement (0 to 25% change). The cream works by stimulating collagen production, but the effect is modest at best for stretch marks.
Professional procedures perform better. Both fractional CO2 laser therapy and microneedling have shown significant reductions in stretch mark size in clinical trials, with improvements measured up to six months after treatment. In a head-to-head comparison, the two approaches produced statistically similar results. Both work by creating controlled micro-injuries in the skin, prompting the body to rebuild collagen in a more organized pattern. Multiple sessions are typically needed, and results vary depending on the age and severity of the marks.
The timing matters more than the method. Treating stretch marks while they’re still in the red or purple stage, when inflammation and remodeling are already underway, gives any intervention a better foundation to work with. Once marks have turned white and the tissue has settled into its scar-like state, improvement is harder to achieve.
When Stretch Marks Signal Something Else
Most stretch marks are cosmetic and harmless. But certain patterns can point to an underlying medical issue worth investigating. Cushing syndrome produces wide, deeply pigmented pink or purple stretch marks, often accompanied by unexplained weight gain around the midsection, a rounded face, thinning arms and legs, and easy bruising. If you’re developing prominent stretch marks without an obvious explanation like weight change, pregnancy, or growth, and especially if they’re accompanied by other symptoms, it’s worth having your cortisol levels checked.
Stretch marks that appear after starting a new medication, particularly corticosteroid creams applied to the same area repeatedly, point to a localized drug effect. The skin changes from topical corticosteroids can include not just stretch marks but also visible blood vessels, increased fragility, and a translucent appearance. These effects are dose-dependent and often reversible if the medication is adjusted early.