The ESK blog
Post-Inflammatory Hyperpigmentation (PIH): What It Is and Why It Happens
24 August 2026
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Written by Dr. Ginni Mansberg
Many people assume that once a pimple, rash or skin injury heals, the problem is over. Unfortunately, skin often leaves behind a reminder in the form of a dark mark that lingers long after the original issue has resolved. These marks are known as rebound pigmentation or in medical jargon: post-inflammatory hyperpigmentation (PIH). It’s one of the most common pigmentary concerns dermatologists see, and one that's frequently misunderstood. PIH isn't a condition that develops on its own; it's a response. It’s your skin's own healing process, slightly overcorrecting.
Let's get into what's actually happening, why some people are far more prone to it than others, and how to tell it apart from the other pigmentation concerns it's commonly confused with.
What Is Post-Inflammatory Hyperpigmentation (PIH)?
PIH occurs when inflammation in the skin stimulates melanocytes - the cells responsible for producing melanin, the pigment that gives skin its colour - to ramp up melanin production during the healing process. The pathophysiology involves complex interactions between inflammatory mediators, melanocytes, and keratinocytes: inflammation resulting from various skin insults, such as acne, eczema, trauma (like insect bites), or dermatologic procedures, triggers the release of inflammatory mediators that activate your melanocytes. The result is a localised overproduction and redistribution of melanin exactly where the original injury or inflammation occurred.
This explains something patients often find confusing: why the dark mark shows up after the spot, rash or wound has already healed, rather than during it. The mechanism involves the release and subsequent oxidation of arachidonic acid into prostaglandins, leukotrienes, and other inflammatory chemicals, which alter the activity of both immune cells and melanocytes specifically, stimulating epidermal melanocytes to increase melanin synthesis and the transfer of pigment to surrounding keratinocytes. While it's well established that an increase in melanin production and distribution within the epidermis and dermis is a hallmark feature of PIH, the exact cellular mechanisms are still not completely understood. Researchers are actively working to map this pathway in more detail.
It's also worth being precise about terminology: PIH is pigmentation, not scarring. PIH is not a disease. It is a wound-healing byproduct, distinct from textural scarring (like the indented or raised scars acne can leave). PIH typically resolves on its own over time, in about 6-12 months. Unless the pigmentation is deeper in the skin’s dermis, which can take years. True scarring involves structural changes to the skin that don't fade the same way.
What does PIH typically look like? Flat (not raised) marks ranging from light brown to dark brown, grey, or even black, appearing exactly where the original inflammation occurred. It is most commonly on the face, but it can develop anywhere on the body that has been injured.
What Causes PIH?
Almost any process that inflames the skin can trigger PIH. Here are the most common culprits:
Acne and Breakouts
Acne is one of the leading causes of PIH, and for good reason. It's both extremely common and inherently inflammatory. Acne vulgaris is a chronic, inflammatory skin disease affecting approximately 80% of young adults and adolescents, and in a 3000 person US based study of acne-related PIH patients, the prevalence was 65% among African American, 48% among Hispanic and 25% among Caucasian patients.
Eczema and Other Inflammatory Skin Conditions
PIH isn't exclusive to acne. PIH is the end result for a variety of inflammatory skin conditions, including atopic dermatitis (eczema) and psoriasis. Any condition that triggers a sustained inflammatory response in the skin carries the same underlying risk.
Skin Injury and Trauma
PIH often occurs in response to a skin injury such as burns or radiation therapy, infection (viral, bacterial, or fungal), or allergic and immunologic reactions including contact dermatitis or insect bite reactions. Essentially, any trauma severe enough to provoke an inflammatory response can leave pigment behind once it's resolved.
Cosmetic Procedures
This one catches people off guard, because the goal of a cosmetic treatment is to improve the skin. But procedures that create controlled inflammation as part of how they work can trigger PIH as a side effect. Up to 92% of patients with Fitzpatrick skin type IV and higher develop PIH following ablative CO2 laser treatment, which is a striking figure and a major reason this risk is taken so seriously in skin-of-colour treatment planning. The same principle applies to peels and microneedling. Basically, any procedure that deliberately creates a controlled injury to stimulate renewal carries some PIH risk, particularly in darker skin.
Picking and Squeezing
Manipulating a spot or scab, like picking, squeezing, or picking at healing skin extends and intensifies the inflammatory process beyond what the original lesion would have caused on its own, which is directly linked to a higher likelihood of pigment being deposited once it heals.
Who Is Most Likely to Develop PIH?
PIH can technically affect anyone, but the risk is very unevenly distributed.
The extent and persistence of PIH depends on the degree of inflammation and how deeply the pigment is stuck in your skin. Darker skin types are way more susceptible due to a greater baseline level of melanin production and more reactive melanocytes. In a systematic review of PIH treatment in skin of colour, across 14 studies summarising 369 people, the main risk factors that emerge from the research are:
- Skin of colour, specifically Fitzpatrick skin types IV–VI (dark skinned people for example from South Asia and lighter skin African descended people) the population in whom PIH is most frequently studied and most clinically significant
- Severe or prolonged inflammatory acne - more inflammation generally means a greater PIH risk
- Chronic inflammatory skin conditions - eczema, psoriasis and similar conditions that involve repeated inflammatory flares
- Repeated skin trauma -including habitual picking, frequent harsh treatments, or repeated injury to the same area
Some people are simply more prone to this response than others, and skin tone is the single most consistent predictor identified in this paper as well as others. See below.
PIH vs Melasma
These two are commonly confused because they can look similar - both can cause brown patches of discolouration on the face. But they're fundamentally different conditions with different causes, and different treatment approaches.
|
|
PIH |
Melasma |
|
Trigger |
Inflammation or injury |
Hormonal fluctuations, UV exposure, heat |
|
Onset |
Develops after a specific inflammatory event |
Develops slowly over weeks, triggered systemically by hormonal fluctuations, UV radiation, and visible light |
|
Pattern |
Localised to the exact site of the original inflammation; can appear anywhere on the body |
Typically symmetrical brown-to-grey macules across both cheeks (the malar pattern) |
|
Depth |
Often closer to the surface, which is why it fades more easily |
Usually penetrates deeper layers of the skin, making it more stubborn |
Unlike melasma, PIH has no hormonal component and is not chronically driven by UV exposure in the same way. Although UV exposure can still make existing PIH worse and slow its fading, which is why sun protection is essential for both conditions.
If you genuinely can't tell which one you're dealing with, that's common. It’s exactly the kind of question worth bringing to a dermatologist or your GP. Your doctor can use a Wood's lamp if they have one to examine your skin to help distinguish between them: epidermal melasma appears as a sharply demarcated brown or black spots under Wood’s light, while dermal pigmentation looks like an unaccented, grey-blue discolouration.
Why Is PIH More Common in Darker Skin Tones?
This comes down to differences in how melanocytes function across skin types. It’s not a difference in how much inflammation occurs, but in how reactively the pigment-producing system responds to it.
Skin of colour individuals (people with Fitzpatrick skin type III–VI) have bigger melanosomes, more active melanocytes, as well as increased eumelanin (dark grey pigment) compared to lighter skin types. Put simply: the melanin-producing machinery in deeper skin tones is both more abundant and more active at baseline, so when inflammation sends the signal to ramp up pigment production, there's simply more capacity for that signal to be acted on, with more melanin produced in response.
Because of this intense reactivity, prevention strategies (gentle, early management of inflammatory conditions, diligent sun protection, avoiding unnecessary trauma) become considerably more important in these skin types, since the margin for triggering a pigmentation response is simply smaller.
Can PIH Be Prevented?
While treatment is a much bigger topic for its own dedicated article, a few prevention principles are worth knowing upfront:
- Manage inflammatory conditions early. The sooner acne, eczema or another inflammatory process is brought under control, the less cumulative inflammation there is to trigger pigment production in the first place. These conditions need to be treated on an ongoing basis- and compliance with your treatment is essential!
- Avoid picking and squeezing. As I’ve mentioned, this directly extends and intensifies inflammation in a way that meaningfully raises PIH risk.
- Reduce unnecessary irritation. Harsh products, over-exfoliation, and aggressive at-home treatments can all create avoidable inflammation.
- Wear sunscreen daily. UV exposure stimulates melanocyte activity broadly, and can both worsen existing PIH and prolong how long it takes to fade.
What Should You Do If You Think You Have PIH?
If you're looking at a dark mark and trying to work out what it is and what (if anything) to do about it, a sensible approach looks like this:
- Think about what triggered it. Can you trace the mark back to a specific spot, rash, or injury? That history is one of the most useful diagnostic clues you have.
- Protect it from UV exposure. Regardless of what the mark turns out to be, sun protection is universally beneficial and will never make things worse.
- Use gentle skincare. You don’t want your skincare to be a part of the problem. Go for barrier builders like niacinamide and ceramides. A gentle low pH balanced cleanser will be gentler on your skin and protect your skin barrier.
- Target multiple pathways. You need to shed the pigmented skin cells that have accumulated- using gentle exfoliators and vitamin A. You also need a tyrosinase inhibitor to switch off the overactive melanocytes. Opt for PHAs over AHAs and go for Retinal instead or Retinol or prescription vitamin A which can cause more irritation- like throwing oil on a grass fire! More on this soon.
- Seek professional advice if you're uncertain, particularly if the mark doesn't fit the typical PIH pattern (for example, if it's appeared without any preceding inflammation, or doesn't seem to be fading at all over many months), since that may point toward melasma or another pigmentary condition needing a different approach.
How is PIH managed?
The most important thing to understand about post-inflammatory hyperpigmentation (PIH) is that you can't successfully treat the pigment without treating the inflammation that caused it in the first place.
If your acne is still active, your eczema isn't controlled or you're still picking at your skin, new pigment will continue to form even while you're trying to fade the old marks.
Step one: Treat the underlying cause
This is where many people go wrong. If acne is causing your PIH, get the acne under control. If eczema or dermatitis is the trigger, repairing the skin barrier and calming inflammation should be your priority. And if you're a picker, breaking that habit is one of the most powerful things you can do for your skin.
No amount of pigmentation treatment can keep up if new inflammation is occurring every day.
Step two: Choose ingredients that target pigment safely
Once the inflammation is under control, focus on ingredients that reduce excess melanin production while encouraging healthy skin renewal.
One of the best-supported ingredients is 4-n-butylresorcinol (4NB). It works by inhibiting tyrosinase, the key enzyme needed to produce melanin. Clinical studies have shown it to be highly effective for treating hyperpigmentation while being well tolerated, even with long-term use.
Meet your new secret weapon against uneven skin tone. Enlighten Gold is a lightweight moisturiser designed to help reduce the appearance of pigmentation. We've blended high strength 4nB (a gentle, and highly effective pigmentation fighter) with PHAs (think of them as a soft exfoliant that plays nice with sensitive skin) and niacinamide to support your skin’s barrier to effectively improve your skin. Whether your skin is oily, dry, or somewhere in between, this pigmentation moisturiser fits right in. Why you'll love it: For best results, use Enlighten Gold in the morning and Ultimate A Gold at night (available together in our Golden Duo). This AM/PM approach targets pigmentation while supporting long-term skin change.
Enlighten Gold
Vitamin A is another excellent option because it speeds up skin cell turnover, helping pigmented cells move through the epidermis more quickly, prevents the transfer of pigment from melanocytes to keratinocytes while also supporting healthier skin overall.
The game-changing night cream developed in partnership with Selma Blair - combines our most potent hero ingredients to effectively and gently tackle the most common skin concerns – in one product. Tackling the signs of aging skin including fine lines, skin elasticity, impaired barrier function, hydration, dullness and uneven skin tone. it is our most powerful product yet and yet it’s still ridiculously well tolerated. Wake up to skin that's supple, smoother, and softer. For the most irritable of skin, Ultimate A may be a better option, particularly when starting to use Retinal based products
Ultimate A Gold
Ultimate A Gold: the most effective and gentle ingredients that evidence based cosmeceutical skincare has to offer, in one revolutionary formula.
*Ultimate A Gold (Retinal) may transfer onto white or light-coloured fabrics. For best results, we recommend using darker clothing or surfaces to avoid visible marks.
Niacinamide or vitamin B3, an antioxidant at a 2% to 5% concentration helps combat pigmentation. It works by inhibiting pigment transfer from melanocytes to keratinocytes. At this concentration, niacinamide also helps heal the skin barrier which can slow down the drivers of PIH.
Repair + is a moisturiser formulated to support skin hydration and barrier function. Its combination of niacinamide, panthenol, hyaluronic acid, and ceramides is designed to help maintain skin moisture, strengthen the barrier function of the skin, reduce the appearance of redness, and support overall skin texture. Key Features:
Repair +
Hydroxy acids have been used in dermatology for decades, and they’re a go-to for lots of different skin concerns. In PIH, they’re thought to help by speeding up how quickly the skin sheds old, pigmented cells, so the excess pigment can clear more easily. However Alpha Hydroxy Acids or AHAs can be irritating to inflamed skin, which can potentially drive further PIH. Newer hydroxyacids known as Polyhydroxy acids or PHAs, such as gluconolactone or lactobionic acid, are non-irritating and suitable for sensitive or inflamed skin.
Introducing our breakthrough skincare solution, the Gentle Glow PHA Serum, designed specifically for those with irritable, red or dry skin! - Reduces the appearance of fine lines and wrinkles and the apparent size of pores. - Helps tackle blemishes and is appropriate for irritable and red skin.
Gentle Glow PHA Serum
Harnessing the power of Polyhydroxy Acids (PHAs), which gently exfoliate and smooth the skin's surface, act as antioxidants and hydrate the skin. Unlike most exfoliation agents, PHAs are very gentle and are not only tolerated on irritable skin, but may also reduce potential irritation from other products in your skincare regimen!
Embrace the journey to a luminous, glowing complexion with the Gentle Glow PHA Serum.
- Smooths, hydrates and plumps the skin.
Why not hydroquinone?
Hydroquinone has been considered the gold standard for treating pigmentation for many years, but it has some important limitations. It can be irritating, particularly for people with sensitive skin or darker skin types who are already prone to PIH. This is because of its potential for skin barrier damage. It also isn't recommended for continuous long-term use because prolonged treatment can rarely lead to ochronosis, a blue-black discolouration of the skin that can be extremely difficult to treat. It must be used for three months to be effective, but most dermatologists suggest cycling off it after a year at most to avoid complications.
By comparison, 4-n-butylresorcinol offers excellent efficacy with a much better safety profile, making it a better choice for ongoing management of pigmentation.
Step three: Avoid creating more inflammation
One of the biggest mistakes I see is people trying to scrub, peel or laser their pigmentation away.
PIH is caused by inflammation, so anything that creates more inflammation has the potential to make it worse. Depending on your skin type and the procedure, this can include aggressive chemical peels, microneedling, IPL and laser treatments. While these procedures have a role in carefully selected patients, they're not the first place I start when treating PIH, particularly in darker skin tones.
Gentle, consistent skincare almost always wins the race.
Step four: Wear sunscreen every single day
Even if your PIH wasn't caused by the sun, UV exposure makes existing pigmentation darker and can prolong recovery. Visible light, particularly blue light, may also contribute in some people with darker skin types.
A broad-spectrum SPF 50+ every morning is one of the simplest and most effective ways to stop new pigment forming while giving existing marks the best chance to fade.
Zinc Shade is a lightweight matte day cream and primer. Its non-greasy, matte finish allows for smooth application and works well under makeup. We spent countless iterations perfecting this lightweight, non-greasy formula to avoid the typical white cast and thick feel of zinc products. The results? A matte finish that works beautifully under makeup. With well tolerated matte finish, it's also well suited to irritable and blemish and bump prone skin. With SPF 15 it also provides broad-spectrum sun protection against UVA and UVB rays. Key features: Lightweight, matte formula suitable for daily use Smooth application with minimal white cast Broad-spectrum UV protection Tested SPF 15 with enhanced UVA coverage Usage: Apply evenly to all exposed areas of skin before sun exposure. Reapply as needed throughout the day.
Zinc Shade
The Bottom Line
PIH develops as a direct result of inflammation. It's your skin's pigment-producing system responding, sometimes a little overzealously, to the healing process. Acne is one of the most common triggers, but eczema, skin injury, cosmetic procedures and even insect bites can all set off the same mechanism. It's distinct from melasma (which is hormonally and UV-driven, not inflammation-driven) and from PIE (aka post-inflammatory erythema, which is about blood vessels, not pigment.) Although all three can sometimes look deceptively similar at first glance. And because of genuine differences in melanocyte behaviour, darker skin tones are considerably more prone to developing PIH, and to it persisting longer once it appears.
Understanding why a mark has appeared is the first real step toward managing it effectively — and toward knowing which of the many available treatment options is actually going to be worth your time.
References
1. Lawrence E, Al Aboud KM. Postinflammatory Hyperpigmentation. StatPearls. NCBI Bookshelf, 2024.
3. Postinflammatory Hyperpigmentation: Practice Essentials, Pathophysiology, Etiology. Medscape.
9. Application of Wood's Lamp in Dermatological and Dental Photodiagnostics. MDPI Sensors, 2025.
10. Melasma vs. PIH: What's the Difference? PSRx clinical overview.
11. PIH vs melasma on face: Spotting the difference. Dr Sheth's clinical overview.