Post-inflammatory hyperpigmentation (PIH) is a flat, darkened patch of skin that forms after an injury or inflammation heals. It’s one of the most common reasons people seek dermatological care, particularly those with darker skin tones. The dark spots aren’t scars, and they aren’t permanent, but they can linger for months or even years depending on how deep the pigment sits in the skin.
Why Skin Darkens After Inflammation
Any time your skin is injured or inflamed, the healing process releases a wave of chemical signals: inflammatory molecules, reactive oxygen species, and growth factors. These signals do more than just repair tissue. They also stimulate melanocytes, the cells responsible for producing melanin (skin pigment), to ramp up production. The excess melanin then spreads into surrounding skin cells, leaving behind a dark spot that persists long after the original inflammation has cleared.
The depth of that pigment matters. When the excess melanin stays in the upper layer of skin (the epidermis), the spots tend to appear tan or brown and generally respond well to treatment. But if the inflammation was severe enough to disrupt the base of the epidermis, pigment leaks down into the deeper layer of skin (the dermis), where it gets trapped. Dermal pigment produces blue-gray or dark brown spots that are harder to treat and take much longer to fade.
What Triggers It
Almost any skin condition that causes inflammation can leave PIH behind. Acne is the most common culprit, but the list is long: eczema, psoriasis, contact dermatitis, insect bites, burns, cuts, and even cosmetic procedures like chemical peels or laser treatments. Picking at or squeezing a pimple makes PIH worse because it deepens the inflammation. Essentially, the more intense and prolonged the inflammation, the darker and more stubborn the resulting spot.
Who Gets It
PIH affects men and women equally, but it’s far more common and more visible in people with darker skin tones. Melanocytes in darker skin are more reactive to inflammatory signals, producing more pigment in response to the same level of injury. People with medium to deep complexions are most frequently affected, though PIH can occur in any skin tone.
PIH vs. Post-Inflammatory Erythema
Not every dark mark after a breakout is PIH. In lighter skin tones (particularly very fair skin), what looks like a lingering acne mark is often post-inflammatory erythema (PIE) rather than true hyperpigmentation. PIE appears as flat pink or red spots caused by damaged or dilated blood vessels, not by excess melanin. A simple way to tell the difference: press a clear glass against the spot. If the color fades under pressure, it’s PIE (a vascular issue). If it stays dark, it’s PIH (a pigment issue). The distinction matters because the two conditions respond to different treatments.
How Long It Lasts
Epidermal PIH, the more superficial type, often fades on its own within 3 to 12 months without any treatment. Dermal PIH is a different story. Because the pigment is trapped deeper, it can take years to resolve and sometimes never fully clears without intervention. Sun exposure slows the fading process for both types, since UV light stimulates further melanin production in already-active melanocytes.
How Dermatologists Assess Depth
One tool dermatologists use is a Wood’s lamp, which shines ultraviolet light on the skin. Epidermal pigment becomes more obvious under the lamp (it “enhances”), while dermal pigment stays the same or becomes less visible. This helps guide treatment decisions and set realistic expectations. However, Wood’s lamp evaluation works best on lighter skin tones and is less reliable for people with very dark complexions.
Sunscreen and Visible Light Protection
Sunscreen is the single most important step in both preventing and treating PIH. But standard sunscreens that only block UV light may not be enough. Visible light, the kind that comes from the sun and even screens, can also trigger pigment production in darker skin tones. In one study, patients using a sunscreen containing iron oxide (which blocks both UV and visible light) alongside a skin-lightening treatment saw a 75% reduction in pigmentation scores, compared to 60% in the group using a UV-only sunscreen. If you’re prone to PIH, look for tinted sunscreens or mineral formulas that list iron oxide as an ingredient. These provide that extra layer of visible light protection.
Topical Treatments
Hydroquinone remains the most studied and effective topical treatment for hyperpigmentation. It works by slowing melanin production directly at the cellular level. Concentrations of 2% are available over the counter in some countries, while 4% formulations, which have the strongest evidence, typically require a prescription. Hydroquinone is often combined with a retinoid and a mild steroid in what’s called triple combination therapy, which is considered a first-line approach.
If hydroquinone isn’t an option or you prefer alternatives, several second-line ingredients have good supporting evidence:
- Azelaic acid (15-20%): Slows pigment production and has anti-inflammatory properties. Well tolerated by most skin types.
- Tranexamic acid (2-5% topical): Originally used to control bleeding, it also interrupts the signaling pathway that triggers melanin overproduction.
- Kojic acid: Derived from fungi, it inhibits a key enzyme in melanin synthesis.
- Cysteamine: A naturally occurring compound that interferes with multiple steps in the pigmentation process.
Whichever ingredient you use, results take time. Most topical treatments need at least 8 to 12 weeks of consistent use before noticeable improvement, and they all work better when paired with daily broad-spectrum sunscreen.
Professional Procedures
For PIH that doesn’t respond to topical treatment, dermatologists may recommend in-office procedures. Chemical peels using glycolic acid can help accelerate turnover in the upper skin layers, pushing out excess pigment. These are typically done every two weeks over a series of sessions.
Laser treatments are another option, but they require caution, especially for darker skin. The near-infrared wavelength (1064 nm) is generally considered the safest choice because it penetrates deeper without damaging the surface of the skin, reducing the risk of triggering new PIH. In small studies, patients treated with this wavelength at low energy settings achieved good clearance over five sessions. Fractional lasers have also shown promise, with one case achieving over 95% clearance in three sessions for post-traumatic hyperpigmentation.
The catch is that lasers themselves can cause PIH, particularly in darker skin tones when used at higher energy settings. This is why dermatologists typically start with conservative settings for patients with more pigment and may combine laser treatment with topical agents and sunscreen to minimize the risk of rebound darkening.
Preventing New Spots
The most effective strategy is reducing the inflammation that triggers PIH in the first place. If acne is the main driver, treating breakouts early and consistently prevents new dark spots from forming. Avoiding picking, squeezing, or scratching inflamed skin makes a significant difference, since mechanical trauma deepens the inflammatory response. And daily sunscreen with both UV and visible light protection keeps existing spots from darkening while your treatment works to fade them.