Acne scars form when inflammation from a breakout damages the deeper layers of your skin, and the repair process produces either too much or too little collagen. About 80 to 90 percent of acne scars are the indented type, caused by a net loss of collagen. The remaining cases involve raised scars from collagen overproduction. How severe your scars become depends largely on how intense the inflammation was and how long it lasted.
What Happens Inside a Breakout
A scar doesn’t start with the pimple you see on the surface. It starts deeper, at the hair follicle. When a pore becomes clogged with dead skin cells and excess oil, it creates a sealed, oxygen-poor environment where bacteria thrive. As these bacteria multiply inside the follicle, your immune system responds by sending waves of white blood cells to the site. Those cells release chemical signals that trigger redness, swelling, and heat, the classic signs of inflammation.
In mild acne, this process resolves on its own without lasting damage. But in more severe cases, particularly deep cysts and nodules, the immune response escalates. Some bacterial strains produce enzymes that actively break down the walls of the hair follicle, spilling infected material into the surrounding skin. At that point, the inflammation is no longer contained in the pore. It spreads into the dermis, the thick structural layer of skin made mostly of collagen, and that’s where permanent damage begins.
Why Inflammation Severity Determines Scarring
Research comparing people who scar to those who don’t has found a clear pattern: scarring is strongly tied to how intense the inflammation is and how long it lasts. In biopsies of acne lesions, people who developed scars had a stronger inflammatory response that took longer to resolve compared to people whose skin healed cleanly. The immune cells linger, continuing to release signals that damage collagen and surrounding tissue.
This is why the same size pimple can leave a scar on one person and not another. It’s not just about the breakout itself but about how aggressively and how long your body fights it. Roughly 95 percent of people with acne develop some degree of scarring, though the severity varies widely. Male sex, younger age at acne onset, and adolescent acne all increase the risk of more severe scars. People whose acne started in adolescence were about 2.7 times more likely to develop significant scarring.
The Repair Process That Goes Wrong
Once inflammation damages the dermis, your body launches a three-stage wound healing process: inflammation, new tissue formation, and remodeling. Each stage involves different cells and chemical signals working in sequence. Scars form when this process doesn’t proceed normally.
During the tissue formation phase, which begins roughly three to five days after the injury, specialized cells called fibroblasts migrate to the damaged area and start producing new collagen. Early on, the replacement collagen is mostly a different type than what was there originally. Over time, the balance is supposed to shift back to match normal skin composition, with about 80 percent of the stronger type I collagen. But in acne lesions, chronic inflammation disrupts this process. Immune cells, including certain white blood cells and mast cells, keep sending signals that push fibroblasts to either overproduce or underproduce collagen, and the remodeling phase never fully corrects the imbalance.
How Indented Scars Form
The vast majority of acne scars are atrophic, meaning they sit below the surrounding skin surface. These form when inflammation destroys more collagen than the body can replace. Inflammatory cells found in 77 percent of atrophic scars suggest that ongoing low-grade inflammation continues to degrade tissue even after the visible breakout has resolved.
Indented scars come in three distinct shapes, each reflecting a different pattern of tissue loss. Ice pick scars are narrow, deep, and V-shaped, extending well into the dermis. They typically result from infected pores where the inflammation tunneled straight down. Boxcar scars are wider with sharply defined vertical edges, like a small crater. They form when inflammation destroys a broader area of collagen near the surface. Rolling scars have gentle, sloping edges that give the skin a wavy or undulating texture. These result from bands of scar tissue pulling the surface of the skin downward from underneath.
How Raised Scars Form
In a smaller number of cases, the repair process overcorrects. Instead of too little collagen, the body produces too much. Fibroblasts differentiate into a more aggressive cell type called myofibroblasts, which keep depositing collagen without stopping. Normally, these cells would die off through a controlled process once the wound is repaired, but defects in that self-destruct mechanism allow them to persist, piling up dense fibrous collagen at the injury site.
This results in hypertrophic scars, which are raised and firm but stay within the boundaries of the original breakout. Keloid scars go further, growing beyond the original wound edges. A pro-fibrotic environment driven by growth factors keeps the collagen production cycle going long after it should have stopped. Keloids are significantly more common in people of African and Asian descent, with incidence as high as 16 percent in Black populations in Africa compared to under 0.1 percent in white European populations.
Genetics and Individual Risk
Your genes play a role in whether your skin scars and how severely. Acne itself is influenced by the interaction of multiple genes and environmental factors, and scarring susceptibility adds another genetic layer on top. Research in Chinese Han populations identified a variation in a gene that controls tissue inhibitors of enzymes responsible for breaking down collagen. People carrying this variation had a higher risk of acne scarring and more severe scars. A separate study found that certain genetic variations in enzymes that degrade structural proteins were more common in people who developed raised, hypertrophic scars after acne.
Family history matters as well. If your parents or siblings scarred from acne, your risk is higher. This likely reflects inherited differences in immune response intensity, collagen production rates, and the efficiency of the remodeling phase.
Scars vs. Post-Inflammatory Marks
Not every mark left behind by a breakout is a true scar. Many people mistake post-inflammatory color changes for permanent scars, and the distinction matters because they resolve very differently. After a pimple heals, you may notice a flat, discolored spot that’s either brown or reddish-purple. Brown marks result from excess pigment deposited in the upper layers of skin, and these tend to fade over weeks to months on their own. Reddish or purple marks come from dilated blood vessels at the healed site and also resolve gradually.
A deeper type of pigment change, where pigment drops into the lower layers of skin, appears blue-gray and can be much more persistent or even permanent. True scars, by contrast, involve a change in skin texture, not just color. If you can feel a depression or a raised bump with your fingertip, that’s structural damage to the dermis, and it won’t resolve without intervention.
Why Early Treatment Matters
Because scarring is directly tied to the duration and severity of inflammation, the most effective prevention strategy is treating acne early and consistently. The longer a breakout persists, the more time the immune response has to damage dermal collagen. Clinical evidence shows that topical treatments combining a retinoid with benzoyl peroxide reduced the formation of new atrophic scars over six months in controlled studies. For mild to moderate acne, topical retinoids or combination products are the standard approach. More severe or nodular acne typically calls for oral treatments to bring inflammation under control faster.
One important caveat: picking, squeezing, or otherwise manipulating acne lesions creates a separate type of mechanical injury with its own healing process. Even good acne treatment won’t prevent scarring from skin picking, which is why avoiding physical manipulation of breakouts is just as important as treating the acne itself.