PIE vs. PIH: Why Your Acne Marks Aren't Fading (and the 5-Second Test to Tell Them Apart)
You finally got your breakouts under control, but your skin still doesn't look clear. Instead of pimples, you're now staring at a map of leftover marks, some red, some brown, that have lingered for weeks or even months. You've tried vitamin C, a brightening serum, maybe a few things you saw go viral, and nothing seems to touch them.
Here's what almost no one tells you: those leftover marks are not all the same thing. And if you're using the wrong products on them, you can brighten and exfoliate for months without seeing a single shade of improvement.
The two most common types of post-acne marks are PIE and PIH. They look different; they come from completely different processes occurring in your skin; and, most importantly, they're treated in nearly opposite ways [1][2]. Learning to tell them apart is the single most useful thing you can do before you spend another dollar on a serum.
One quick reassurance first: PIE and PIH are marks, not true acne scars. True scars involve a change in texture, a pit or a raised area. PIE and PIH are flat changes in color, and flat marks are far more treatable than textured ones.
Two Kinds of Marks, Two Different Problems
When an acne lesion heals, it can leave behind discoloration through one of two very different mechanisms. One involves your blood vessels. The other involves your pigment. Telling which is which is the whole game, because the fix for one essentially does nothing for the other.
PIE: The Red, Pink, and Purple Marks
Post-inflammatory erythema (PIE) is the term used for the pink-to-red discoloration that lingers after an inflamed breakout heals [2]. It's actually a fairly new term in the dermatology literature, introduced specifically because the redness left behind by acne needed its own name, separate from brown discoloration [2].
Here's what's actually happening underneath: when a pimple becomes inflamed, the tiny blood vessels (capillaries) beneath it dilate and become damaged. As the skin heals, those vessels stay visible at the surface, leaving a flat red, pink, or purplish mark exactly where the blemish used to be. So PIE is not a pigment problem at all. It's a vascular one. It's about blood vessels, not melanin.
PIE tends to show up most readily on lighter skin tones, where redness contrasts easily against the surrounding skin, though anyone can develop it, and picking at a blemish makes it far more likely.
PIH: The Brown, Tan, and Gray Marks
Post-inflammatory hyperpigmentation (PIH) is the flat brown, tan, or grayish discoloration left behind after inflammation [1]. This is the one most people mean when they say "dark spots" or "acne marks."
PIH is a pigment problem. When your skin is inflamed, whether by a breakout, picking, or an overly aggressive treatment, it signals your melanocytes (your pigment-producing cells) to ramp up melanin production; that extra melanin settles into the area and leaves a stubborn dark mark. If you've read my breakdown of the "pigment switch" and the enzyme tyrosinase, this is the same process in action, just triggered by inflammation rather than sun exposure. (You can read that one here.)
Unlike PIE, PIH disproportionately affects deeper skin tones. In fact, uneven pigment is one of the most common reasons people with richer skin tones seek out a dermatologist, and PIH in skin of color tends to be both more frequent and more persistent [1][3]. This is exactly why a careful, gentle approach matters so much, which I'll come back to.
The 5-Second Test You Can Do at Home.
Color is a good first clue: reddish leans PIE, brownish leans PIH. But color alone can fool you, especially if you have a medium or tan skin tone where marks can read as both. So here's a simple at-home check (it's a home version of a clinical technique called diascopy):
Press gently on the mark with something clear; the side of a clean drinking glass works, and watch what the color does.
If the mark turns white and disappears under pressure, then refills with color when you let go, it's PIE. Pressing briefly pushes the blood out of those dilated vessels, so the redness vanishes for a moment.
If the color stays put no matter how you press, it's PIH. Melanin doesn't move when you apply pressure.
That five-second test tells you more about how to treat your marks than almost any product label will.
And if you have both at once? That's extremely common; a red mark with brown edges is a classic mixed picture, particularly in medium and tan skin. If that's you, you'll want to address both pathways rather than picking one.
Why Treating Them Backward Wastes Months
Here's the part that genuinely frustrates me on behalf of my clients: most people are handed the same generic "just brighten it" advice no matter what kind of mark they have. But because PIE and PIH come from different sources, they respond to opposite treatments [1][2][4].
Brightening and pigment-blocking ingredients (the ones designed to shut down melanin) do nothing essentially for PIE, because there's no excess melanin to address. It's blood vessels.
Soothing, vascular-focused approaches do nothing to fade PIH, because the problem there isn't redness; it's pigment that's already been deposited.
So if you've been diligently using a vitamin C or a pigment corrector on red marks and wondering why they won't budge, this is almost certainly why. You've been treating the wrong mechanism the whole time.
How to Actually Fade PIE (the red marks)
The encouraging news about PIE is that it often improves on its own over time as the damaged vessels heal [4]. Your job is mostly to stop making it worse and to support that healing:
Get the acne itself under control first. Every new inflamed breakout is a chance to create a fresh red mark, so calming active acne is step one [2].
Protect your barrier and stop picking. Picking and squeezing deepen vascular damage and prolong redness.
Be realistic about topicals. Gentle, anti-inflammatory ingredients like niacinamide and azelaic acid help calm the skin and the underlying inflammation, but no cream "erases" a blood vessel.
For stubborn PIE, the most effective option is in-office. The pulsed dye laser (PDL) is considered the gold standard here because it specifically targets the blood vessels responsible for the mark and is the approach best supported by research for post-acne erythema [2][4].
How to Actually Fade PIH (the dark marks)
PIH responds to a completely different toolkit, one aimed at calming inflammation and interrupting melanin production [1][3]:
Start early and treat the inflammation. The sooner you address both the breakout and the pigment, the faster PIH resolves and the less you create in the first place [1].
Use tyrosinase inhibitors. These are the ingredients that turn down melanin production at the source: azelaic acid, kojic acid, arbutin, hydroquinone, and others [1]. Azelaic acid is a particular favorite of mine for post-acne marks because it fades pigment and calms acne at the same time, which makes it ideal when you're fighting both. (I go deeper on azelaic acid and combination pigment correction in this post.)
Support cell turnover. Retinoids and other resurfacing agents help move pigmented cells along and are well-established options for PIH [1][3].
Consider professional treatment for stubborn cases. In-clinic chemical peels can speed up the fading of recalcitrant PIH, but, and this is critical in deeper skin tones, they have to be done carefully, because overly aggressive treatment can actually trigger more pigment [1][3]. This is where working with a professional matters far more than chasing the highest percentage you can find online.
The One Rule That Applies to Both: Sunscreen
No matter which type of mark you're dealing with, sunscreen is non-negotiable, and it's the step people skip most.
UV exposure darkens and prolongs PIH, and sun makes both types of marks linger longer and risk becoming more stubborn. And it isn't only UV: visible light, the light from the sun and even your screens, along with long-wavelength UVA, has been shown to worsen both pigmentation and redness, which is why a basic clear sunscreen isn't always enough for pigment-prone skin [5].
For anyone actively treating marks, especially PIH, I recommend a tinted mineral SPF. The iron oxides that give tinted formulas their color also help shield the skin from visible light, protection that untinted sunscreens don't provide [6]. If you're putting in the work to fade your marks, daily SPF is what protects that progress.
When to Get a Professional Eye on It
If you've been guessing, treating every mark the same way, and watching months pass without change, that's usually the sign it's time to stop experimenting. A proper assessment can tell you exactly which marks are PIE, which are PIH, whether you have both, and what your skin can actually tolerate, so your routine finally works with your skin instead of against it.
At Advanced Precision Aesthetics, helping clients sort out exactly this is a huge part of what I do: identifying the kinds of marks you're dealing with and building corrective plans for acne, post-acne marks, and hyperpigmentation tailored to your skin and skin tone. Advanced Precision Aesthetics offers luxury aesthetic services in Chevy Chase, Maryland, so the entire process takes place in the comfort of your own home.
If your post-acne marks have overstayed their welcome, book an appointment and let's build a plan that targets the right problem.
References & Footnotes
Davis, E. C., & Callender, V. D. (2010). Postinflammatory hyperpigmentation: A review of the epidemiology, clinical features, and treatment options in skin of color. Journal of Clinical and Aesthetic Dermatology, 3(7), 20–31.
Bae-Harboe, Y.-S. C., & Graber, E. M. (2013). Easy as PIE (Postinflammatory Erythema). Journal of Clinical and Aesthetic Dermatology, 6(9), 46–47.
Chaowattanapanit, S., Silpa-Archa, N., Kohli, I., Lim, H. W., & Hamzavi, I. (2017). Postinflammatory hyperpigmentation: A comprehensive overview — Treatment options and prevention. Journal of the American Academy of Dermatology, 77(4), 607–621.
Kalantari, Y., Dadkhahfar, S., & Etesami, I. (2022). Post-acne erythema treatment: A systematic review of the literature. Journal of Cosmetic Dermatology, 21(4), 1379–1392.
Kohli, I., et al. (2018). Synergistic effects of long-wavelength ultraviolet A1 and visible light on pigmentation and erythema. British Journal of Dermatology, 178(5), 1173–1180.
Lyons, A. B., Trullas, C., Kohli, I., Hamzavi, I. H., & Lim, H. W. (2021). Photoprotection beyond ultraviolet radiation: A review of tinted sunscreens. Journal of the American Academy of Dermatology, 84(5), 1393–1397.