What post-inflammatory hyperpigmentation is, and why melanin-rich skin is hit hardest

Post-inflammatory hyperpigmentation (PIH) is the dark mark that remains after skin has been inflamed — by acne, eczema, an insect bite, a wound or a procedure. It is not a separate disease. It is the visible record of inflammation that has already resolved.

The pattern the clinical reviews describe

Post-inflammatory hyperpigmentation disproportionately affects darker skin tones. In skin of colour, post-inflammatory hyperpigmentation is often more distressing than the acne itself.

That last point matters practically. It is common for someone to clear their breakouts and then feel that the treatment has failed, because the thing they still see is the mark. Acne lesions improve weeks before post-inflammatory hyperpigmentation resolves, so the two problems are on different timelines and are not measuring the same thing.

In the fetched 2024 systematic review of 48 studies and 1,356 individuals, 78% of affected individuals were female and the mean age was 29. Those demographics describe who was studied. They are not a market survey of African women and are not presented as one.

Why the mark outlasts the cause

Inflammation stimulates melanocytes to overproduce melanin. That melanin deposits in the epidermis and dermis, and in deeper skin tones the response tends to be stronger and longer-lasting. The injury itself heals in days or weeks. The pigment that responded to it can take considerably longer to clear.

What this means for a routine

The practical reading of this evidence is narrow but useful: if the inflammation is still active, clearing it is the first priority, because every new lesion starts a new clock on the pigment it leaves behind. The pigment that is already there is a separate problem with a separate timeline.

This is also why advice that treats PIH as a single product problem tends to disappoint. A routine that prevents new inflammation but does not address existing pigment will look like it is doing nothing for months, because the marks are still there while the pimples have gone.

When the mark is not the problem

Some marks are not PIH at all. Melasma is a distinct condition with a distinct pattern, and a spot that changes shape, bleeds, or does not behave like a post-inflammatory mark should be assessed rather than treated with a routine.

Seek medical evaluation for worsening melasma, post-inflammatory hyperpigmentation that has not responded after three to six months of consistent care, and anything suspected to be skin cancer. Prescription-strength treatments — including topical retinoids, hydroquinone 4% and prescription azelaic acid 20% — require appropriate medical supervision and are never routine first-line recommendations.