Stretch marks form when your skin stretches faster than it can adapt, causing structural breaks in the deeper layer of skin called the dermis. They affect the majority of women during puberty and pregnancy, and they’re common in anyone experiencing rapid growth, weight gain, or muscle building. Understanding what actually happens beneath the surface helps explain why some people get them and others don’t.
What Happens Inside Your Skin
Your skin has two main layers: a thin outer layer (epidermis) and a thicker structural layer underneath (dermis). The dermis contains a network of collagen and elastin fibers that give skin its strength and ability to bounce back after stretching. When your body grows or expands faster than these fibers can keep up with, they break apart.
The process starts with immune cells in the skin releasing enzymes that break down elastin in the middle of the dermis. Once the elastin dissolves, collagen fibers reorganize in a disorganized pattern, similar to scar tissue. The result is a visible line on the surface where the skin has become thinner and structurally weaker than the surrounding area. This is why stretch marks feel slightly indented when you run your fingers over them.
The Most Common Causes
Puberty
Growth spurts during adolescence are the single most common trigger. About 70% of adolescent girls and 40% of boys develop stretch marks during puberty. They typically show up on the thighs, buttocks, and breasts in girls, and on the lower back and thighs in boys, corresponding to the areas where the body grows fastest during those years.
Pregnancy
Roughly 56% of women develop stretch marks during their first pregnancy. The abdomen is the most obvious site, but they also appear on the breasts, hips, and thighs as the body changes shape. The rapid expansion of the belly in the second and third trimesters puts enormous continuous stress on the skin’s connective tissue.
Weight Gain
Gaining a significant amount of weight over a short period stretches the skin beyond its elastic limit. The faster the gain, the more likely stretch marks are to form. They tend to appear wherever fat accumulates most, commonly the abdomen, hips, and upper arms.
Rapid Muscle Growth
Bodybuilders and athletes who put on muscle quickly are prone to stretch marks, particularly on the front of the shoulders, lower back, and thighs. The direction of the marks follows the direction of the mechanical force pulling on the skin, so they’re usually linear and parallel. Prolonged heavy lifting over time also contributes, even without dramatic size changes.
Why Hormones Matter
Mechanical stretching alone doesn’t fully explain stretch marks. Hormones, particularly cortisol, play a significant role. Cortisol weakens the elastic fibers in your skin, making the dermis more vulnerable to tearing even under normal levels of stretch. This is one reason stretch marks are so common during puberty and pregnancy, when hormone levels shift dramatically.
People with Cushing syndrome, a condition where the body produces too much cortisol, develop 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 appear without any obvious weight gain or growth. If you notice large, vividly colored stretch marks appearing without a clear cause, it’s worth having your cortisol levels checked.
Prolonged use of corticosteroid creams or oral corticosteroids can produce the same effect, thinning the skin and reducing its ability to handle stretching.
The Role of Genetics
If your mother had stretch marks, you’re more likely to get them. A large genome-wide study identified four regions of DNA significantly associated with stretch mark risk. The strongest link was near the gene responsible for producing elastin, the protein that gives skin its snap-back quality. Variants near this gene were associated with stretch marks both in the general population and specifically in pregnant women.
Certain inherited connective tissue conditions make stretch marks almost inevitable. Marfan syndrome and a related condition called congenital contractural arachnodactyly are caused by mutations in genes that produce components of elastic microfibrils, the tiny structural cables that reinforce skin. People with these conditions develop stretch marks easily, often in unusual locations and at a young age, because their skin’s structural scaffolding is fundamentally weaker.
How They Change Over Time
Stretch marks go through two distinct phases. When they first appear, they’re red, pink, or purple. This early stage reflects active inflammation and increased blood flow in the damaged area. Over time, sometimes months, sometimes a year or more, the color fades. The marks become pale, whitish, and slightly shiny, with a scar-like texture. At this point, the inflammation has resolved, and what remains is essentially a flat, atrophic scar.
This color progression matters for treatment. Early-stage marks, while they’re still red or purple, are more responsive to topical treatments. Once they’ve faded to white or silver, the skin has fully remodeled and becomes much harder to improve.
Do Creams and Oils Actually Work?
Many people reach for cocoa butter, olive oil, or specialty creams during pregnancy or periods of growth, hoping to prevent stretch marks. The evidence is disappointing. A clinical trial found that olive oil did not significantly reduce either the incidence or severity of stretch marks during pregnancy compared to using nothing at all. While women who used olive oil had slightly fewer severe marks, the difference was not statistically meaningful. Cocoa butter has been studied with similarly underwhelming results.
For marks that have already formed, tretinoin (a prescription vitamin A derivative) and glycolic acid have shown clinical improvement, but primarily on recent, still-red stretch marks. A systematic review of stretch mark treatments found that current evidence doesn’t support any single treatment as clearly effective, and many studies in the field are small and low quality. Keeping skin well-moisturized may improve comfort and appearance slightly, but it won’t prevent the structural damage happening deeper in the dermis.
Who Is Most at Risk
Several factors stack to increase your likelihood of developing stretch marks:
- Family history: Genetic variants affecting elastin production significantly raise your risk.
- Age: Younger skin, paradoxically, is more susceptible. Adolescents and younger pregnant women develop stretch marks at higher rates.
- Speed of change: The faster you grow, gain weight, or build muscle, the less time your skin has to adapt.
- Cortisol levels: Higher cortisol from stress, medical conditions, or medication use weakens skin structure.
- Starting size: In pregnancy, women with higher pre-pregnancy weight and those carrying larger babies tend to develop more stretch marks.
Stretch marks are not a sign of anything wrong with your skin. They’re an extremely common response to normal life events, from growing up to growing a baby. Most people have them somewhere on their body, whether or not they’ve noticed.