How Do Acne Scars Form?

Acne scars are the result of tissue damage caused by inflammatory acne.

Overview

The vast majority of acne scars are caused by from persistent cases of inflammatory acne affecting the same area of skin. Individuals who suffer from frequent nodular and cystic acne outbreaks (Acne Types: 3-4) are at a very high risk of developing permanent acne scarring. This is particularly true when a region is affected by overlapping acne outbreaks, with no opportunity for the skin to completely heal.

When an individual experiences persistent outbreaks of severe inflammatory acne, significant regions of the affected skin and underlying tissue can be damaged. Acne is an inflammatory process that usually involves an infection caused by bacteria (eg. Propionibacterium acnes).

The inflammation that occurs during severe acne prevents the body from mobilizing the cells and materials necessary for the normal healing process that is required to repair the skin. In this situation, the original (healthy) tissue can be replaced by fibrous scar tissue.

The Role of Inflammation in Acne Scarring

What many people may not realize is that acne scarring is primarily due to the body’s own immune response to infection, and not the infection itself. A major component of inflammatory acne is the migration of white blood cells to the hair follicle, sebaceous glands and surrounding tissue. These white blood cells compose much of the “pus” that comes out when you pop a zit.

The white blood cells that make up the pus in acne pimples, nodules and cysts are not uniform. Instead the pus contains a mixture of many different sub-types of white blood cells, such as macrophages, neutrophils, dendritic cells, T cells, granulocytes, mast cells and others. Neutrophils are one of the body’s front-line defenses against infection and these cells are usually the most abundant white blood cells in an acne lesion.

Many of the white blood cells (and especially neutrophils) produce powerful degradative enzymes that can damage health tissue. These cells also produce inflammatory molecules, super-oxides and free radicals. These weapons are designed to help neutralize pathogens and foreign invaders, but they can also cause damage to the surrounding healthy tissue.

In inflammatory acne, the damage caused by these white blood cells can actually cause the underlying bacterial infection to spread, leading to more inflammation and tissue damage. This can create a vicious, self-fulfilling cycle of tissue damage that leads to permanent acne scars.

Neutrophils and Acne Scars

When it comes to scarring, perhaps the most important type of white blood cell is the neutrophil. The neutrophil is one of the first responders to the infected follicle, and can accumulate in great numbers. Neutrophils are kind of like the suicide bombers of the cellular world. When they reach the site of infection they can undergo apoptosis (controlled suicide) and degranulation, which releases many anti-microbial molecules, DNA and proteases into environment. These proteases that can cause tremendous damage to the surrounding tissue, which ultimately results in scarring. The proteases digest the elastin and collagen matrix that provides support and elasticity to the skin.

The Structure of Scar Tissue

Healthy skin is supported by a complex matrix (scaffolding) that provides structural support and nutrients to the skin surface. When skin is damaged, this matrix helps guide the healing process. Without this matrix to guide healing, the body has a very difficult time properly repairing and re-creating the damaged tissue.

In cases of persistent infection and inflammation, the body is not able to repair the matrix fast enough to keep up with the damage. In these cases, the body begins to build scar tissue, which is simple and tough. The scar tissue can permanently replace the more complex and delicate healthy matrix. This process underlies not only the formation of acne scars, but of other diseases marked by chronic inflammation, such as chronic obstructive pulmonary disorder (emphysema) and rheumatoid arthritis.

Scar tissue is composed largely of collagen, which is the same material that comprises much of a healthy sub-cutaneous matrix. However, unlike the healthy matrix – which is a complex, spacious and interconnected web of collagen and other proteins – the collagen in scar tissue is much different. In scar tissue, the collagen becomes tightly bundled and tends to line up in a single direction, instead of the original, interconnected web pattern.

In scar tissue there is much less open space than healthy tissue, and many of the essential accessory proteins and molecules that are essential for the maintenance of healthy skin are absent. This alignment of the collagen fibers and their closely packed arrangement creates a denser, less elastic tissue.

Scar tissue becomes impermeable to migration by many cell types, preventing the formation of blood vessels and a regrowth of complex structures, such as hair follicles and sweat glands. This is why scar tissue is generally monotone, feels tough and dense to the touch, and is hairless. It also explains why the body has such a difficult time replacing scar tissue with healthy tissue.

Repairing Scar Tissue

Once scar tissue has been generated at a site of injury, it is relatively permanent (without medical intervention). In some cases, the body will gradually replace some scar tissue with the healthy tissue, but this process is so slow that is largely irrelevant. The single best treatment for acne scarring, is to prevent it in the first place. This means aggressively attacking the infection and treating the inflammation as it arises.

Fortunately, there are many different treatments available to help repair acne scar damage. The ideal type of treatment is largely dependent on the specific types of acne scarring. Acne scar treatment generally involves either surgically removing the scar tissue, or breaking it apart with laser, heat or surgical treatments.

Light and Laser treatments can be very effective treatments for many different kinds of acne scars. Invasive and non-invasive surgical treatments can also be very helpful.

Topical Retinoids may also be helpful for very mild acne scars and uneven skin tone.

References

Physiopathology of acne vulgaris: recent data, new understanding of the treatments. Pawin, et al. 2004.
Topical ALA Photodynamic Therapy for the Treatment of Acne Vulgaris. Hongcharu, et al. 2000.
Human b Defensin-1 and -2 Expression in Human Pilosebaceous Units: Upregulation in Acne Vulgaris Lesions. Chronnell, et al. 2001.
A prospective, randomized, placebo-controlled, double-blinded, and split-face clinical study on LED phototherapy for skin rejuvenation: Clinical, profilometric, histologic, ultrastructural, and biochemical evaluations and comparison of three different treatment settings. Lee, et al. 2007.
Acne scarring: a classification system and review of treatment options. Jacob, et al. 2001.
The role of elastic fibers in scar formation and treatment. Cohen, et al. 2017.
The pivotal role of inflammation in scar/keloid formation after acne. Shi, et al. 2017.
Mechanical stress and the development of pseudo‐comedones and tunnels in Hidradenitis suppurativa/Acne inversa. Boer, et al. 2016.
Effect of basic fibroblast growth factor combined with laser on content of a variety of cytokines in acne scar wound. Dong, et al. 2016.
Scar prevention and remodeling: a review of the medical, surgical, topical and light treatment approaches. Kerwin, et al. 2014.
Post acne scarring: a review. Goodman, et al. 2003.
The molecular basis of keloid and hypertrophic scar formation. Tuan, et al. 1998.
Postacne scarring: a review of its pathophysiology and treatment. Goodman, et al. 2000.
Acne scar treatment. Rusciani, et al. 2015.
Acne scar treatment: a multimodality approach tailored to scar type. Zaleski-Larsen, et al. 2016.
Atrophic scar formation in acne patients involves long‐acting immune responses with plasma cells and alteration of sebaceous glands. Carlavan, et al. 2018.
The pivotal role of inflammation in scar/keloid formation after acne. Shi, et al. 2017.
Prospective Study of Pathogenesis of Atrophic Acne Scars and Role of Macular Erythema. Tan, et al. 2017.
Expression of inflammatory and fibrogenetic markers in acne hypertrophic scar formation: focusing on role of TGF-β and IGF-1R. Yang, et al. 2018.
The role of elastic fibers in scar formation and treatment. Cohen, et al. 2017.
Current Concepts in Acne Pathogenesis: Pathways to Inflammation. Tan, et al. 2018.

The Types of Acne Scars

Acne scars come in many different shapes, sizes and even colors.

Each type of acne scar has its own unique characteristics and features. Because of these differences, the best treatment for acne scars varies from person to person. It is important to carefully choose the treatment that best matches your needs in order to achieve optimal results.

Acne scars can be classified into three main groups:

  • Depressed (pitted scars)
  • Raised (keloid scars)
  • Discoloration scars

Depressed (Pitted) Acne Scars

Depressed scars are the most common type of scarring that results from inflammatory acne. Depression acne scars rest on top of a patch of fibrous, collagen rich scar tissue. This fibrous tissue anchors the base (bottom) of the scar to the sub-cutaneous tissue, maintaining the depression and preventing the regrowth of healthy tissue.

Effective treatments for depressed acne scars usually involve disrupting or removing this scar tissue to allow the body to replace it with functional, healthy tissue.

There are three main types of depressed acne scars:

  • Rolling Scars
  • Boxcar Scars
  • Icepick Scars

Rolling scars

Rolling acne scars are relatively broad depressions in the skin that have rounded, sloping edges. The presence of many of this types of scar in a region of skin gives it a rolling appearance, hence the name.

Rolling scars are common for in individuals who have had patches of skin that have been afflicted by long-term inflammatory acne. They tend to become more pronounced as the skin ages and loses its original elasticity and fullness.

Because rolling scars have sloping edges, many of the available scar treatment techniques are capable of producing positive results. Laser resurfacing (ablative and non-ablative), chemical peels, micro-dermabrasion, needling, subcision and even red light phototherapy can produce improvements in the appearance of rolling scars. Cosmetic fillers are also occasionally used, but many times the large size of the affected area makes fillers an unappealing option.

Boxcar scars

Boxcar acne scars are also relatively broad depressions, but they have steep, defined edges.

Because box car scars have steeper edges than rolling scars, it is more difficult to smooth them out and blend them into the surrounding skin. Laser resurfacing, particularly ablative laser resurfacing (eg. Er:YAG, Nd:YAG, CO2) often produces good results. Multiple laser treatments may be necessary to achieve maximum improvement for patients with significant scarring.

Box car scars often cover smaller areas than rolling scars and can be better candidates for cosmetic fillers. Shallow box car scars can be treated with chemical peels and/or micro-dermabrasion, but these treatments are not very effective for deep scars. Surgical options include punch- out excisions, needling and surgical subcisions.

Icepick scars

Icepick acne scars are deep and narrow scars. In many cases, icepick scars resemble a large, empty pore in the skin.

Ice pick scars are often the most difficult type of acne scar to treat without surgical procedures. Ice pick scars are often quite deep, making them very difficult to treat with standard resurfacing techniques. Chemical peels, micro-dermabrasion and many types of laser resurfacing are unlikely to have a significant impact on ice pick scars because those techniques do not remove enough tissue to be effective.

Some laser treatments may be effective at disrupting the underlying scar tissue. Because ice pick scars are quite narrow, punch-out excisions are a popular, mildly invasive and effective treatment technique.

Hypertrophic and Keloid Scars

Hypertrophic (Keloid) scars occur when excess scar tissue forms at the site of the injury. Hypertrophic scars are regions of fibrous and firm scar tissue which is raised relative to the surrounding healthy tissue. These scars present a set of different challenges than depressed scars and are addressed with different treatments.

When scar tissue forms in great excess, it can become a large nodule of dense, rubbery scar tissue that is known as a keloid. The development of hypertrophic and keloid scars is less common in acne patients than the development of depressed scars. A number of factors can potentially be involved in the process, including acne severity and duration, genetics and secondary infections.

Because hypertrophic acne scars are raised, they can often be treated with ablative laser resurfacing and micro-dermabrasion. They can also be surgically removed. Hypertrophic scars are generally less responsive to treatments like chemical peels, because the scar tissue is much more resistant to the ingredients in a chemical peel than healthy tissue.

Discoloration and Pigmentation Scarring

The tissue damage caused by inflammatory acne can cause many abnormal conditions in the skin. One of the most common types of long-term form of acne scarring is the abnormal discoloration of the skin.

Hyper-pigmentation

Hyper-pigmentation is a condition where elevated levels of the pigment melanin accumulate in the skin. This creates the appearance of freckle-like spots or blotches. Hyper-pigmentation occurs when melanocytes (the cells that produce the melanin pigment) begin to proliferate at the site of injury, or when an existing population of melanocytes begins to produce excess amounts of melanin. Both of these events can result from the trauma caused by an inflammatory acne lesion.

Hyper-pigmentation is often treated with light and laser treatments that specifically target melanin, such as KTP Lasers, Pulsed Dye Lasers (PDL), and Intense Pulsed Light (IPL) therapy. Hyperpigmentation is also addressed with the prescription medications like hydroquinolone, which inhibits the production of melanin, and topical Retinoids, which increase the rate of cellular turnover in the skin.

Hypo-Pigmentation

Hypo-pigmentation occurs when melanocytes are depleted from the injury site or lose their ability to produce melanin. Hypopigmentation is common in areas of skin that have been replaced with scar tissue, which tends to have a light, pinkish appearance. It can also occur in otherwise healthy looking regions of skin.

Hypo-pigmentation is generally more noticeable in those individuals with darker base skin tones. Vitiligo is a condition in which melanocytes lose the ability to produce melanin. There are not many effective treatments available for hypo-pigmentation, although chemical peels and laser resurfacing may be helpful for some individuals.

Erythema (Permanent Redness)

Erythema is a condition in which small capillaries near the surface of the skin become damaged or permanently dilated. This condition presents as a region of redness in the skin. Individual capillaries may be visible, or the area may have general redness. Erythema is somewhat common in acne patients and is most visible in patients with lighter skin tones.

Erythema may be treated with topical prescription medications to decrease vasodilation, but the results are generally temporary. Erythema generally responds well to laser and light based treatments that selectively target hemoglobin, such as Argon and Pulsed Dye Lasers. Red Light Phototherapy may also be a useful treatment for erythema in some individuals.

References

Acne Scars: Pathogenesis, Classification and Treatment. Fabbrochini, et al. 2010.
Resurfacing of Different Types of Facial Acne Scar With Short-Pulsed, Variable-Pulsed, and Dual-Mode Er:YAG Laser. Woo, et al. 2004.
Resurfacing the Acne Scarred Face. Fulton, et al. 1999.
The Management of Post-Acne Scarring. What are the Options for Treatment? Goodman, et al. 2000.
Acne scarring: A review and current treatment modalities. Rivera, 2008.
Acne scarring: A classification system and review of treatment options. Jacob, et al. 2001.
Effective Treatments of Atrophic Acne Scars. Gozali, et al. 2015.
Acne scar treatment: a multimodality approach tailored to scar type. Zaleski-Larsen, et al. 2016.
Acne scarring: A review of available therapeutic lasers. Cohen, et al. 2016.
Fractional CO2 lasers for the treatment of atrophic acne scars: A review of the literature. Magnani, et al. 2014.
Safety and efficacy of microdermabrasion in the treatment of skin disorders: A systematic review. Asgharzadeh, et al. 2017.
Evaluation of microneedling fractional radiofrequency device for treatment of acne scars. Chandrashekar, et al. 2014.
Chemical peels in active acne and acne scars. Kontochristopoulos, et al. 2017.