The development of an acne scar is due to the body's natural response of healing a pimple. The body must replace tissue that was damaged by the pimple, and this process can sometimes become imbalanced, leading to a scar.
More specifically, replacing this tissue is a highly intricate process that involves balancing the activity of proteins that stimulate or inhibit collagen production. When the activity of these proteins becomes imbalanced, the body produces either too little or too much collagen, leaving behind either an indented or raised scar.
Why does this occur more in some people than others? Research suggests that weaker but more chronic inflammation during the pimple healing process, as well as genetics, may make certain individuals more susceptible to acne scarring than others.
Patients suffering from acne, particularly more severe acne, very often develop some amount of scarring. In fact, researchers investigating the prevalence of scarring in 185 acne patients treated at an acne clinic found that 95% had scarring somewhere on their face or body.1
Scarring occurs on the body more frequently in males than in females, while scarring on the face is equally common in males and females. However, not everyone is equally prone to acne scarring. Individual differences in the immune system and genetics help explain why certain individuals are more susceptible to scarring than others.
Types of Acne Scars
The pimple healing process can produce three types of acne scars:
- Atrophic (indented) scars are sunken due to a significant loss of an important skin protein called collagen. Often, these scars are given specific names, like "ice-pick" scars, "rolling" scars, or "boxcar" scars, based on the appearance and depth of the skin damage. These are much more common than hypertrophic scars.
- Hypertrophic (raised) scars are raised due to a significant gain of collagen.
- Superficial macular scars are temporary "scars" that involve a darkening of the skin after the acne lesion heals. This is also called hyperpigmentation. There is some controversy over whether these are really scars since they fade with time - generally within 3 - 18 months.2
Steps from Pimple to Scar
Acne scar formation occurs in 4 steps:
1. Initial clogged pore
The surface of the body is covered with microscopic hair follicles that produce tiny hairs along with skin oil. These follicles, often called pores, can become clogged.2
2. Formation of an acne lesion
Once a pore becomes clogged, skin oil - which normally drains to the surface - is trapped inside and accumulates. Acne bacteria thrives on this skin oil and multiplies inside the skin. The pore expands, and the wall of the pore breaks within the skin. The immune system responds with inflammation, which consists of redness, swelling, and an infiltration of white blood cells. This forms a run-of-the-mill "pimple" or "zit."2,3 If the clogged pore ruptures into deeper layers of the skin, it can develop into a larger, severe inflamed acne lesion like a nodule or cyst. Any type of inflamed acne lesion can scar, but nodules and cysts are more prone to scarring.
3. Tissue repair
The body uses inflammation to clean up debris. This cleaning process often results in damage of nearby healthy cells and tissues. After the inflammation subsides, the body begins repairing the cellular and tissue damage, which it does by stimulating the production of an important skin protein, collagen.4
4. Skin tissue remodeling
The amount of collagen the body produces controls the formation of a scar. If the body produces too little collagen, atrophic (indented) scars will form. If the body produces too much collagen, hypertropic (raised) scars will form.
Here comes the deep science: The body controls collagen production through two proteins: matrix metalloproteinases (MMPs) and MMP inhibitors. MMPs are proteins that degrade collagen, and MMP inhibitors are proteins that prevent MMPs from degrading collagen. If the body produces too many MMPs, then an abundance of collagen is degraded, which results in atrophic scars. But if the body produces too many MMP inhibitors, then collagen can build up and form hypertrophic scars. In summary, a pimple will scar when the body fails to balance the amount of MMPs and MMP inhibitors, resulting in the production of too little or too much collagen.4
Why Some People Scar More than Others
The natural pimple healing process can vary greatly between individuals. Researchers have attempted only a few studies that try to identify these differences and understand why certain people are more prone to develop acne scars than others. This research has focused on examining the (1) immune system and (2) genetics of people who are more prone to acne scarring.
Immune system and inflammation
The immune system controls inflammation in our bodies. Research has found that the immune system can control the response to repairing the skin after a pimple.
People who are not prone to acne scarring show a strong initial inflammatory response that is effective at quickly cleaning up acne debris. After cleaning up, this inflammatory response returns to normal levels.
People who are prone to acne scarring have a different immune response, which includes weaker and delayed inflammation that is not as effective at cleaning up acne debris. This weaker immune response must therefore be maintained for longer periods of time in order to clear the debris, but chronic inflammation can be damaging to the skin tissue and cause acne scarring.5
Research has attempted to identify genes associated with acne scars by investigating populations of people who are more prone to develop them.
Three studies have identified three different genes that may be associated with the formation of acne scars. Scientists have observed that the first gene is found more often in patients prone to acne scarring and believe that it is connected with skin cell growth and clogged pores.6 Researchers found that the second identified gene was also present more often in patients prone to acne scarring, but the gene's function remains unknown.7 Finally, scientists found a location on a genetic structure called a chromosome containing many genes that they believe are involved in acne scar formation.8
Overall, the research only weakly links these three genes with acne scarring. However, the findings promote the idea that genetics is one explanation for why some people are more prone to acne scarring than others. Scientists need to perform more research to confirm these findings, as well as to identify other potentially associated genes.
The Bottom Line
Whether you are prone to scarring or not is most likely not something you can change. The best course of action when it comes to acne scarring is to prevent acne in the first place.
An important thing to note here, however, is that picking at the skin can cause more scarring than a pimple itself. Therefore, it is absolutely imperative that you NEVER PICK at a healing acne lesion. If you want to pop a pimple, do that carefully and correctly, but never, ever pick at your skin.
The Experts at Acne.org
Our team of medical doctors, biology & chemistry PhDs, and acne experts work hand-in-hand with Dan (Acne.org founder) to provide the most complete information on all things acne. If you find any errors in this article, kindly use this Feedback Form and let us know.
1. Layton, A. M., Henderson, C. A. & Cunliffe, W. J. A clinical evaluation of acne scarring and its incidence. Clin Exp Dermatol 19, 303 - 308 (1994).
2. Goodman, G. J. Post-acne scarring: a short review of its pathophysiology. Australas J Dermatol 42, 84 - 90 (2001).
3. Goodman, G. J. Postacne scarring: a review of its pathophysiology and treatment. Dermatol Surg 26, 857 - 871 (2000).
4. Fabbrocini, G. et al. Acne scars: pathogenesis, classification and treatment. Dermatol Res Pract 2010, 1 - 13 (2010).
5. Holland, D. B. et al. Inflammation in acne scarring: a comparison of the responses in lesions from patients prone and not prone to scar. Br J Dermatol 150, 72 - 81 (2004).
6. Navarini, A. A. et al. Genome-wide association study identifies three novel susceptibility loci for sever acne vulgaris. Nat Commun 5, 4020 (2014).
7. Zhang, M. et al. A genome-wide association study of severe teenage acne in European Americans. Hum Genet 133, 259 - 264 (2014).
8. He, L. et al. Two new susceptibility loci 1q24.2 and 11p11.2 confer risk to severe acne. Nat Commun 5, 2870 (2014).
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