Acne scars form when inflamed breakouts damage the deeper layers of skin, and the body’s repair process either produces too little or too much collagen to fill the wound. About 80 to 90 percent of acne scars are the depressed, indented type caused by a net loss of collagen. The remaining cases involve raised scars from collagen overproduction. Nearly 95 percent of people with acne develop some degree of scarring, making it one of the most common lasting effects of the condition.
How a Breakout Becomes a Wound
Every acne lesion starts with a clogged pore. Dead skin cells get trapped inside the pore, oil builds up, and bacteria multiply. In mild cases like small whiteheads, the blockage resolves without much fuss. But when the clog goes deeper and bacteria thrive, the immune system mounts an aggressive response. White blood cells flood the area within one to three days, releasing chemicals that kill bacteria but also damage the surrounding tissue in the process.
This is where the trouble starts. The immune cells don’t just target bacteria. They release enzymes that chew through collagen and elastin, the structural proteins that give skin its firmness and bounce. A family of these enzymes, called matrix metalloproteinases, specifically targets collagen types I and III, which are the main structural proteins in skin. One enzyme in particular acts as an upstream “gatekeeper,” initiating the breakdown of collagen fibers into smaller fragments. In a normal, shallow pimple, this destruction is limited and the skin can rebuild. In deep, inflamed cysts or nodules, the damage extends far into the dermis, and a clean recovery becomes much harder.
Why the Skin Can’t Always Rebuild
After the initial inflammation winds down (usually within a few days), the body shifts into repair mode. Specialized cells called fibroblasts move in and begin laying down new collagen to fill the gap left by the destroyed tissue. This rebuilding phase lasts anywhere from about four days to three weeks, followed by a remodeling phase that can stretch out over a full year as the body fine-tunes the repaired area.
The problem is that this repair process rarely restores the skin to its original state. When the inflammation was deep or prolonged, the fibroblasts simply can’t produce enough new collagen to replace what was lost. The result is a depression or pit in the skin, an atrophic scar. Inflammatory cell infiltrates have been found in 77 percent of these depressed scars, confirming that ongoing low-grade inflammation continues to interfere with the healing process even after the breakout itself has cleared.
How Raised Scars Form
In a smaller percentage of cases, the repair process overcorrects. Instead of too little collagen, fibroblasts produce too much. This happens when a signaling molecule called TGF-beta 1 stays elevated for too long. Under normal conditions, TGF-beta 1 tells fibroblasts to build new tissue and then steps back. In hypertrophic scars, TGF-beta 1 activity is prolonged, which does three things simultaneously: it pushes fibroblasts to keep producing collagen, it transforms some fibroblasts into a more aggressive cell type that deposits even more structural material, and it suppresses the enzymes that would normally break down excess collagen. The result is a firm, raised scar that sits above the surrounding skin.
Raised scars are more common along the jawline, chest, and back, areas where the skin is thicker and under more tension during healing.
Three Types of Depressed Scars
Not all indented scars look the same, and the differences come down to how deep the inflammation went and what happened during healing.
- Ice pick scars are narrow, deep, and V-shaped. They result from deep cystic acne that destroys collagen far beneath the skin surface. Because the damage channel is so narrow and deep, the skin has very little surface area to regenerate from, making these the most stubborn type to treat.
- Boxcar scars are wider depressions with sharply defined vertical edges, almost like a small crater. They form when inflammatory acne destroys collagen over a broader area and the skin simply cannot regenerate enough structure to fill the gap.
- Rolling scars have a different mechanism entirely. Rather than a simple loss of collagen, fibrous bands of scar tissue form between the skin’s surface and the deeper tissues beneath it. These bands pull the skin downward at irregular intervals, creating a wavy, uneven texture.
What Makes Scarring Worse
The single biggest predictor of scarring is the severity of the acne itself. In one large clinical study, higher global acne severity was significantly linked to both the presence and the severity of scars. Among patients with severe acne, the vast majority progressed to moderate or severe scarring. The relationship is straightforward: deeper, more inflamed lesions cause more tissue destruction, leaving the skin with a bigger deficit to repair.
Delayed treatment compounds the problem considerably. In the same research, patients who had never received any acne treatment all developed moderate to severe scarring, with two-thirds ending up in the severe category. Chronic, untreated inflammation gives enzymes more time to degrade collagen and gives the immune system more time to cause collateral tissue damage. One study found that patients treated with the most effective oral medication had severe scarring rates of about 9 percent, compared to nearly 38 percent among those treated with less aggressive therapy.
Men tend to be at higher risk, partly because they often wait longer to seek treatment. In one study, the average duration of active acne before treatment was over eight years in men compared to about six years in women. Stress also plays a measurable role. Statistical analysis identified stress levels as a significant independent risk factor for developing scars, likely because stress hormones increase oil production and inflammation. Genetics matter too: variations in genes that control TGF-beta signaling can influence both acne severity and the body’s tendency to scar.
Why Timing Matters So Much
Once an acne scar fully matures, which happens over the course of months to a year as the remodeling phase completes, the structural change is essentially permanent. The collagen deficit in a depressed scar or the fibrous bands in a rolling scar won’t resolve on their own. This is why the most effective strategy for preventing scars is treating active acne early and aggressively enough to prevent deep inflammation from taking hold in the first place.
The window for prevention is during the active breakout phase. Every week that a deep, inflamed lesion persists is another week of enzyme activity breaking down collagen. Picking or squeezing lesions worsens the damage by rupturing the pore wall deeper into the dermis, spreading bacteria and inflammation into surrounding tissue. Topical steroid misuse has also been shown to delay healing and increase scarring by thinning the skin and suppressing the normal repair response.
For scars that have already formed, treatment options work by restarting the wound healing process in a controlled way. Techniques like laser resurfacing deliver thermal energy to stimulate fibroblasts to produce new collagen and elastin, essentially giving the skin a second chance at the repair it failed to complete the first time around. The specific approach depends on the scar type, since ice pick scars, boxcar scars, and rolling scars each involve different structural problems at different depths.