Post-inflammatory hyperpigmentation (PIH) is darkening of the skin that appears after an injury or inflammation heals. It happens because the inflammatory process triggers melanocytes, the cells that produce your skin’s pigment, to go into overdrive and deposit excess melanin in the surrounding skin. The result is a flat, darkened patch that lingers long after the original wound, pimple, or rash has resolved. It can affect anyone, but it is most common and most visible in people with medium to deep skin tones.
How Inflammation Triggers Dark Spots
When your skin is injured or inflamed, immune cells flood the area and release signaling molecules called cytokines. Several of these cytokines directly stimulate melanocytes to produce more melanin than usual. The extra melanin gets packaged into tiny structures called melanosomes and shuttled from melanocytes into the surrounding skin cells through several transfer methods, including membrane fusion and a process where skin cells essentially engulf the melanin packages.
Not all inflammatory signals push pigment production in the same direction. Some cytokines promote melanin production while others suppress it. The balance tips toward darkening when pro-pigment signals dominate, which is why some types of inflammation leave marks and others don’t. The depth of the inflammation also matters: if the injury disrupts the junction between the outer skin layer and the deeper dermis, melanin can drop down into the dermis, where it is much harder for the body to clear.
Common Causes
Almost any skin inflammation or injury can leave PIH behind. The most frequent triggers are acne, eczema flares, sunburns, cuts and scrapes, allergic reactions, and skin rashes like psoriasis. Cosmetic procedures, insect bites, and even aggressive use of skincare products can set it off. The key factor isn’t the type of injury so much as how much inflammation it generates and how deep that inflammation reaches.
Who Gets It and Why Skin Tone Matters
PIH can occur in all skin types, but it shows up most noticeably in people with Fitzpatrick skin phototypes III through VI, roughly corresponding to medium, olive, brown, and deep brown skin. Darker skin contains more active melanocytes, so the inflammatory cascade has more pigment-producing machinery to overstimulate. The severity depends on several factors: your baseline skin color, how deep and intense the inflammation was, and how stable your melanocytes are in response to injury.
This susceptibility creates a frustrating catch-22 with certain treatments. Aggressive procedures like medium-depth chemical peels and ablative laser treatments carry a real risk of triggering new PIH in darker skin types. One study found that 92% of patients with Fitzpatrick type IV skin developed PIH after ablative fractional laser treatments, compared to just 23% of patients with lighter skin types. That doesn’t mean these treatments are off the table, but they require careful supervision and strong sun protection protocols.
PIH vs. Post-Inflammatory Erythema
People often confuse PIH with post-inflammatory erythema (PIE), but they are fundamentally different. PIH is caused by excess melanin and appears as brown or dark spots. PIE is caused by dilated blood vessels near the skin’s surface and appears as pink or reddish marks. On lighter skin, the distinction is fairly obvious: brown spots versus red or pink ones. On darker skin, both can simply look like areas darker than your natural tone, making them harder to tell apart visually.
There’s a simple test you can do at home. Press a clear glass firmly against the spot. If the color fades momentarily and then returns when you release, you’re looking at PIE, because the pressure temporarily pushes blood out of those dilated vessels. If the color doesn’t change at all with pressure, it’s PIH. This distinction matters because the two conditions respond to different treatments.
Epidermal vs. Dermal PIH
Dermatologists sometimes use a UV light called a Wood’s lamp to determine how deep the excess pigment sits. When the melanin is in the epidermis (the outermost skin layer), the dark patch appears sharply defined under the lamp and looks brown or black. When melanin has dropped into the dermis, it looks grey-blue and less distinct under the lamp. Epidermal PIH responds better and faster to topical treatments. Dermal PIH is considerably more stubborn because the melanin is trapped deeper, where topical products have limited reach and the body’s natural clearing process is slower.
How Long It Takes to Fade
Epidermal PIH often fades on its own over several months to a year, especially if the original inflammation was mild and the skin is protected from further sun exposure. Dermal PIH can persist for years or, in some cases, become permanent without treatment. The timeline varies widely depending on your skin type, how deep the pigment sits, and whether you’re consistently protecting the area from UV and visible light exposure.
Topical Treatments That Help
Several ingredients can speed fading by interrupting melanin production at different stages. Hydroquinone remains the most widely studied option. It works by directly inhibiting the enzyme that produces melanin. Over-the-counter formulations are available at lower concentrations, while stronger versions require a prescription.
Retinol accelerates skin cell turnover, which helps shed pigmented cells faster, and it also blocks the enzyme involved in melanin production. Vitamin C is an antioxidant that reduces melanin synthesis and can help prevent new dark spots from forming. Kojic acid works by blocking the production of tyrosine, an amino acid the skin needs to manufacture melanin. Azelaic acid is available without a prescription at concentrations under 10%, while stronger formulations (15% to 20%) require one. Many dermatologists recommend combining two or more of these ingredients for better results than any single product delivers alone.
Professional Procedures
Chemical peels using glycolic acid or salicylic acid have shown good results for facial PIH. They work by removing the outermost layers of pigmented skin in a controlled way, and they are generally considered safe and cost-effective. Superficial peels carry less risk of triggering new pigmentation than deeper peels, which is an important consideration for people with darker skin. Medium-depth peels are typically not recommended for Fitzpatrick skin types IV and above because the risk of worsening pigmentation outweighs the benefit.
Laser treatments are sometimes used for stubborn PIH, but they carry significant risk of paradoxical hyperpigmentation, particularly in darker skin tones. Any professional procedure for PIH should be paired with strict sun protection and close follow-up to catch early signs of rebound darkening.
Why Standard Sunscreen Isn’t Enough
Sun protection is the single most important factor in both preventing and treating PIH. Ultraviolet light stimulates melanocytes, which can darken existing spots and trigger new ones. But UV isn’t the only concern. Visible light, the kind that comes from the sun and indoor lighting, also drives pigmentation in medium and dark skin tones.
Standard mineral sunscreens containing zinc oxide or titanium dioxide block UV effectively but do relatively little against visible light. Research published in the Journal of Drugs in Dermatology found that sunscreens containing iron oxides significantly outperformed a mineral SPF 50+ sunscreen at preventing visible light-induced pigmentation in people with Fitzpatrick type IV skin. Tinted sunscreens and foundations containing iron oxides serve a dual purpose: they mask existing dark spots cosmetically while also preventing the visible light exposure that would make them worse. Broad-spectrum sunscreens combining iron oxides with traditional UV filters have been shown to improve pigmentation after eight weeks and help prevent relapse over six months.
For anyone dealing with PIH, switching to a tinted sunscreen with iron oxides and reapplying it throughout the day is one of the simplest and most effective steps you can take.