Scars are areas of fibrous tissue that replace normal tissues after any injury or disease. It is a natural process of wound healing.
There are two types of healing processes: regeneration and repair.
The liver and the epidermis of the skin heal by regeneration, i.e. multiplication of cells to restore original structure and function. This type of healing leaves no scars. However most organs in humans, including the dermis of the skin, heal by repair, i.e. deposition of fibrous tissue, in order to maintain continuity of tissues. This process of repair leads to scar formation. Scar formation can be atrophic with loss of tissue, or hypertrophic, with excess tissue. In acne, scarring is more commonly atrophic leading to depressions and uncommonly hypertrophic leading to elevated scars.
Why does Acne Scar?
Acne is an inflammatory process that extends into the dermis, hence scarring occurs early. In the noninflammatory phase, when there are only comedones, there is no scarring. Once the noninflammatory lesion evolves into an inflammatory lesion, the mechanisms of wound healing are activated.
If the inflammation is extensive and deep, extending into the deep dermis
and continues untreated, scarring results. The different types of scars
in acne are a result of the extent, depth and degree of inflammation
that is followed by repair. A study compared the histopathological and
immunohistochemical features of acne
lesions that were prone to scarring versus those that did not scar.
It was found that a predominantly specific immune response was present in patients prone to scarring, which was initially smaller and ineffective, but was increased and activated in resolving lesions.
Excessive inflammation in healing tissue was conducive to scarring. In contrast, lesions that did not scar showed a large and active nonspecific inflammatory response (few memory T cells) in early lesions, which subsided quickly when the lesion was resolving.
Hence controlling inflammation early is probably the key to prevent or reduce scarring in acne.
When does Acne Scar?
Scarring in acne begins early and can affect 90 percent of patients depending on the severity of acne and delay in treatment. To understand the pathophysiology of acne scars, it is first essential to understand the
pathogenesis of acne.