Post-inflammatory hyperpigmentation (PIH) shows up as flat, discolored patches on the skin where inflammation once occurred. The marks range from tan to dark brown, or in deeper cases, blue-gray to almost black. They are not raised, bumpy, or textured differently from the surrounding skin. If you’re looking at a dark spot left behind after a pimple, bug bite, burn, or rash, and that spot is completely flat and smooth to the touch, you’re almost certainly looking at PIH.
Color Varies by Skin Tone and Depth
The color of PIH depends on two things: your natural skin tone and how deep the pigment sits. When excess melanin is trapped in the upper layers of skin (the epidermis), the marks appear tan, brown, or dark brown. This is the most common form and what most people notice after acne breakouts or minor skin injuries.
When inflammation is more severe or prolonged, it can damage the boundary between the upper and lower layers of skin. Melanin then drops into the dermis, the deeper layer, where immune cells called macrophages absorb it. This creates a blue-gray or grayish-black hue that looks distinctly different from the warm brown tones of surface-level PIH. You might see this deeper type after severe eczema flares, chemical burns, or aggressive cosmetic procedures.
On lighter skin, PIH can also appear pink or reddish before deepening to brown. On medium to dark skin tones, the marks tend to be noticeably darker than the surrounding skin, sometimes appearing almost black. The contrast is generally more visible in people with darker complexions, which is one reason PIH is reported more frequently in skin of color.
Shape, Size, and Texture
PIH marks are medically described as macules, meaning flat spots that you can see but cannot feel. Run your finger over a PIH mark and the skin feels identical to the skin around it. There’s no roughness, scaling, or raised edge. This is one of the easiest ways to distinguish PIH from an active pimple, a scar with texture changes, or a condition like psoriasis that leaves thickened patches.
The shape and size of PIH perfectly mirrors the original inflammation. A round pimple leaves a round dark spot. A long scratch leaves a linear streak. A widespread rash like pityriasis rosea can leave scattered bluish-brown macules across the trunk. This pattern-matching quality is actually one of the key features that helps identify PIH. If someone can recall the injury, rash, or breakout that preceded the dark mark, the distribution should line up exactly.
What Triggers It
Any inflammation in the skin can leave PIH behind. The most common triggers include acne (especially inflamed cysts and pustules), eczema, psoriasis, allergic reactions, insect bites, cuts, scrapes, and burns. Cosmetic procedures like chemical peels, laser treatments, and microdermabrasion can also cause it, particularly in people with darker skin tones.
The underlying mechanism is straightforward: inflammation releases signaling molecules and reactive oxygen species that stimulate melanocytes, the pigment-producing cells in your skin, to go into overdrive. These cells produce excess melanin and transfer it to surrounding skin cells, where it accumulates and creates visible darkening. The more intense or prolonged the inflammation, the more melanin is produced and the deeper it can penetrate.
How Long PIH Lasts
Surface-level PIH (the tan-to-brown type) can take months to years to fade on its own without any treatment. It does resolve eventually in most cases, but “eventually” can mean six months for a light mark or several years for a deep brown one. Sun exposure slows the process significantly because UV light stimulates further melanin production in the affected area.
Dermal PIH, the blue-gray variety where pigment has dropped into deeper skin layers, is a different story. It may either be permanent or resolve over a very long period. Because the melanin is trapped inside immune cells in the dermis, the body’s ability to clear it is limited compared to surface pigment that gradually sheds with normal skin turnover.
How to Tell PIH From Scarring
People often confuse PIH with scars, but they’re fundamentally different. A scar involves structural damage to the skin itself, creating indentations (like ice-pick or boxcar acne scars) or raised tissue (like keloids). PIH involves no structural change at all. The skin’s architecture is intact; only its color has changed. This distinction matters because PIH, being a pigment problem rather than a tissue problem, is generally more treatable and more likely to improve over time.
If you press a glass slide against a PIH mark and it doesn’t blanch (turn lighter with pressure), the discoloration is from melanin rather than from dilated blood vessels. Redness that blanches with pressure is more likely post-inflammatory erythema, a related but different condition caused by damaged blood vessels rather than excess pigment. Post-inflammatory erythema is more common on lighter skin and appears pink or red rather than brown.
Treatment Options
There is no single gold-standard treatment for PIH, but several approaches can speed fading. Topical products that slow melanin production are the most common first step. These include ingredients like hydroquinone, azelaic acid, niacinamide, retinoids, and alpha hydroxy acids like glycolic acid. Combination formulas that pair a pigment-lightening agent with a retinoid tend to work faster than single ingredients alone.
Chemical peels using glycolic or salicylic acid can accelerate the turnover of pigmented surface skin cells. For deeper or stubborn PIH, certain laser treatments have shown effectiveness, though lasers must be used carefully on darker skin tones because they can paradoxically trigger more PIH if settings aren’t calibrated correctly.
Regardless of treatment, daily sunscreen is the single most important step for anyone dealing with PIH. Unprotected sun exposure can darken existing marks and undo months of progress. A broad-spectrum SPF 30 or higher, applied consistently, helps prevent the affected melanocytes from producing even more pigment while the skin heals.