Skin Care Education

Post-Inflammatory Hyperpigmentation

The flat, darkened discolouration that develops in the skin following an inflammatory event such as acne, eczema, or injury. A pigmentation change rather than a structural scar, and one that gradually fades over time.

What Is Post-Inflammatory Hyperpigmentation?

Post-inflammatory hyperpigmentation, commonly abbreviated to PIH, is the flat, darkened mark that remains on the skin after an inflammatory event has resolved. When the skin experiences inflammation, whether from acne, eczema, a cut, a burn, an insect bite, a procedure, or any other cause of skin irritation or injury, the melanocytes in the affected area respond to the inflammatory stimulus by producing excess melanin during the healing process. This excess melanin is deposited in the skin and remains as a flat dark mark after the inflammation itself has subsided.

PIH is one of the most common skin concerns across all ages, skin types, and skin tones. It is important to be clear about what PIH is and what it is not. PIH is a pigmentation change, a flat discolouration with no change to the skin’s surface texture or structure. It is not a scar. A scar involves a structural change to the skin, such as a depression, pit, raised area, or thickened tissue. This distinction matters because PIH, as a purely pigmentation-based change, has the capacity to fade over time, whereas true structural scars do not.

PIH affects people of all skin tones but its prominence, persistence, and clinical significance vary considerably. Medium to deeper skin tones have a higher baseline melanocyte density and a greater capacity for melanin production in response to inflammatory triggers. This means that PIH in these skin tones tends to be more pronounced, more deeply deposited, and longer-lasting than in lighter skin tones, where it may fade more readily. This variability is one of the reasons that skin tone is a critical consideration in approaching PIH.

Causes and Contributing Factors

Factor	Description
Inflammatory skin events	Any inflammatory process in the skin can trigger PIH by stimulating melanocyte activity in the affected area. Acne is the most common cause in everyday practice, but eczema flares, contact dermatitis reactions, insect bites, cuts, abrasions, burns, and other forms of skin injury or irritation can all produce PIH during the healing process.
Acne lesions	Inflammatory acne, including papules, pustules, and deeper nodules and cysts, is one of the most frequent and consistent producers of PIH. The more inflamed the acne lesion, the more intense the melanocyte response tends to be and the darker and more persistent the resulting mark.
Picking and manipulation	Picking, squeezing, or otherwise manipulating inflamed spots introduces additional mechanical trauma to an already inflamed area. This additional injury intensifies the inflammatory response and substantially worsens the resulting PIH, making marks darker, larger, and longer-lasting than they would have been without manipulation.
Skin tone	The melanocyte density and reactivity of the skin is significantly influenced by skin tone. Darker skin tones have more numerous and more active melanocytes, which respond to inflammation with a more intense pigment production. This is why PIH is characteristically more pronounced, more deeply deposited, and more persistent in medium to deeper skin tones.
UV exposure	UV radiation stimulates melanocyte activity throughout the skin, including in areas where PIH marks are present. Sun exposure darkens existing PIH marks and slows their natural fading process. Consistent sun protection is one of the most important factors in allowing PIH to fade and in preventing existing marks from deepening.
Certain skincare products and procedures	Products or procedures that cause skin irritation or inflammation can trigger PIH, particularly in more reactive skin types or in individuals with medium to deeper skin tones where melanocyte reactivity is higher. This is a relevant consideration when selecting and introducing new skincare actives or professional treatments.
Hormonal influences	Hormonal activity can increase baseline melanocyte sensitivity, making the skin more prone to pronounced PIH in response to inflammatory triggers. This can be a contributing factor in hormonally active periods such as pregnancy.

Frequently Asked Questions: Post-Inflammatory Hyperpigmentation

No, and this distinction is clinically important. Post-inflammatory hyperpigmentation is a flat pigmentation change with no structural alteration to the skin’s surface. There is no depression, pit, raised area, or textural change. It is a mark caused by excess melanin deposition during the healing process and, given sufficient time and appropriate management, it will fade. A true acne scar, such as a rolling scar, boxcar scar, or ice pick scar, involves a physical structural change to the skin, creating a permanent depression or alteration in its surface. True scars do not fade. PIH and structural acne scars can coexist on the same individual, but they are fundamentally different in nature and require different approaches.

This varies significantly depending on skin tone, the depth of the pigment deposit, the intensity of the original inflammation, and how consistently sun protection is used. In lighter skin tones with superficial PIH, marks may fade noticeably within several months with consistent SPF use. In medium to deeper skin tones, or where the pigment has been deposited more deeply in the dermis rather than just the epidermis, marks can persist for a year or considerably longer without targeted management. The rate of fading is also influenced by whether ongoing triggers such as recurring acne or continued UV exposure are present, as these can maintain or deepen marks that would otherwise be fading.

UV radiation is one of the most significant factors in maintaining and deepening PIH marks. When UV reaches the skin, it stimulates melanocyte activity broadly, including in areas where PIH pigment is present. This UV stimulation can darken existing marks and actively counteract the natural fading process. Consistent broad-spectrum sun protection reduces the UV stimulus to melanocytes in affected areas, allowing the marks to fade at their natural rate without being replenished by ongoing UV-driven pigment production. SPF use is widely considered the most important single measure in supporting PIH to fade and preventing treated or improving marks from darkening again.

The marks themselves do not recur once the pigment has been cleared. However, if the inflammatory trigger returns to the same area, such as a recurrence of acne in the same location, new PIH will develop in response to the new inflammatory event. The tendency to develop PIH in response to inflammation is a characteristic of the skin and melanocyte reactivity rather than of specific locations on the face. Managing the underlying cause of inflammation, such as treating acne effectively to reduce the frequency and severity of lesions, is therefore as important as managing the resulting PIH marks.