What Post-Inflammatory Hyperpigmentation Actually Is, and Why Deeper Skin Marks More Readily

What is that dark mark left behind after a pimple heals? It is not a scar in the structural sense. It is a patch of extra pigment your own skin manufactured while it was healing, and dermatology has a specific name for it: post-inflammatory hyperpigmentation, or PIH. "Postinflammatory hyperpigmentation (PIH) is a reactive hypermelanosis that develops following cutaneous inflammation. Common causes of PIH include intrinsic skin conditions (e.g., acne and eczema) as well as external insults to the skin, such as burn injuries and dermatologic procedures." ¹ Any injury that triggers inflammation can trigger this response afterward, a popped pimple, an insect bite, a scrape, even a chemical peel done too aggressively.

Why melanin-rich skin responds harder

The same review continues plainly: "PIH more commonly occurs in individuals with darker skin, for whom it is often a source of significant psychological distress." ¹ That is not a coincidence of who happens to get acne. It comes down to the biology of the melanocyte itself, the cell that makes pigment. A molecular review of PIH in dark skin explains it at the cellular level: "the degree of skin pigmentation is correlated with the size of melanocytes, in dark skin, the cells are significantly enlarged and transfer more melanosomes to the epidermis due to higher tyrosinase activity." ² Larger melanocytes, a more active pigment-producing enzyme, more melanin handed off to the surrounding skin cells. When inflammation shows up and asks those cells to respond, they respond with more raw material already on hand.

There is a second layer to it. The same paper notes that "individuals with darker skin could be also more prone to changes in the inflammatory profiles that are linked to low-grade chronic expression of the pro-inflammatory cytokines." ² The inflammatory signaling that tells melanocytes to ramp up pigment production is already running a little hotter in deeper skin, so a single breakout can leave more of a mark than the same breakout would on lighter skin.

The numbers, stated plainly

A current clinical reference puts a figure on how common this actually is: "The incidence of postinflammatory hyperpigmentation in individuals with darker skin tones with acne can be as high as 65%." ³ Nearly two out of three people with acne and deeper skin tones will deal with a mark left behind, on top of dealing with the acne itself. The same source is blunt about the pattern that follows from the mechanism above: "The darker the skin color, the more intense and persistent hypermelanosis tends to be." ³

Not the same thing as a scar, and not the same thing as melasma

It helps to be precise about what PIH is not. It is not a true scar, meaning it does not involve the loss or distortion of skin structure the way an ice-pick or boxcar acne scar does. It is a color change sitting on top of otherwise normal skin, which is part of why it responds to topical treatment at all. It is also a different condition from melasma, the patchy facial pigmentation linked more closely to hormones and chronic sun exposure, even though the two are sometimes confused and even though some of the same treatments help both. A 2026 review of PIH describes it as "a common pigmentary disorder that is especially prevalent among individuals with skin of color," ⁴ a useful reminder that this is a well recognized clinical entity with its own name and its own literature, not a vague catch-all for any dark patch on the face.

What this means, and what it does not

This is a cosmetic concern, not a diagnosis, and it is also not a flaw in your skin. It is your skin's healing machinery doing exactly what it is built to do, at a volume that happens to be higher in melanin-rich skin. Knowing that the mark is a response, not a wound and not a scar, and that the response is biologically explainable rather than random, is the starting point for treating it patiently rather than panicking about it or assuming it says something is wrong with your skin.

References

1. Kaufman BP, Aman T, Alexis AF. Postinflammatory hyperpigmentation: epidemiology, clinical presentation, pathogenesis and treatment. Am J Clin Dermatol. 2018, 19(4):489-503. PMID 29222629. doi.org/10.1007/s40257-017-0333-6
2. Markiewicz E, Karaman-Jurukovska N, Mammone T, Idowu OC. Post-inflammatory hyperpigmentation in dark skin: molecular mechanism and skincare implications. Clin Cosmet Investig Dermatol. 2022, 15:2555-2565. PMID 36466945. doi.org/10.2147/CCID.S385162
3. Lawrence E, Syed HA, Al Aboud KM. Postinflammatory hyperpigmentation. In: StatPearls. Treasure Island (FL): StatPearls Publishing. Updated November 25, 2024. www.ncbi.nlm.nih.gov/books/NBK559150/
4. Persson C, Desai R, Manikkuttiyil C, Multani H, Lirio R, Nueva M, Hesari R, Gupta A. Post-inflammatory hyperpigmentation in skin of color: emerging therapies and treatment algorithms. Cureus. 2026, 18. PMID 42153065. doi.org/10.7759/cureus.107234