You finally got your breakouts under control. What's left behind isn't a pimple, it's a flat mark that just won't fade, no matter how much vitamin C or spot-fading serum you throw at it. Here's the thing nobody tells you: there are two completely different marks acne leaves behind, and if you're treating the wrong one, you could be spinning your wheels for months.
Red or pink marks are PIE (post-inflammatory erythema), caused by damaged blood vessels under the skin. Brown, tan, or gray marks are PIH (post-inflammatory hyperpigmentation), caused by excess pigment. They need different treatments, and using a PIH-focused routine on PIE (or the reverse) can stall your progress or make things worse. The good news: one ingredient, azelaic acid, has real trial evidence for treating both at once.
What's Happening Under Your Skin
PIE happens when inflammation from a breakout damages the tiny blood vessels near the skin's surface. Those vessels stay dilated and visible even after the breakout itself is gone, which is what you're seeing as redness. PIH works completely differently: inflammation triggers your skin to produce extra melanin in the area, and that excess pigment is what shows up as a brown or gray mark. Same starting point, a breakout, two entirely different repair processes happening underneath.
PIE or PIH? The Key Clues
| Clue | PIE | PIH |
|---|---|---|
| Color | Pink or red | Brown, tan, or gray |
| The blanch test | Lightens or disappears when you press on it | Stays the same when pressed |
| More common in | Lighter skin tones | Darker skin tones |
| Gets worse from | Heat, friction, sun | Sun exposure specifically |
How to Confirm Which One You Have
1Press on it
If it lightens or disappears under pressure, that's PIE. If the color stays put, that's PIH.
2Check the color against the table above
Pink or red points to PIE, brown or gray points to PIH.
3Track it for two weeks
Note whether heat and friction make it worse (PIE) or whether sun exposure is the main trigger (PIH).
4If you genuinely can't tell, that's useful information too
Many people have both at once, and a dermatologist can confirm it faster than weeks of guessing.
How to Avoid New Marks in the First Place
- Don't pick, pop, or squeeze breakouts. That single habit is one of the most direct ways to trigger both PIE and PIH, since it deepens the inflammation that causes each one.
- Treat active acne early and gently rather than waiting it out. The longer a breakout stays inflamed, the more likely it leaves a mark behind.
- Wear sunscreen daily, even over active breakouts. Sun exposure worsens both PIE and PIH, and it's the one trigger that's fully within your control.
How to Treat PIE
Azelaic acid has real trial evidence here: a randomized, placebo-controlled study using the 15% prescription-strength gel found it measurably reduced the vascular markers behind PIE within 8 to 12 weeks. Niacinamide and consistent sun protection also help calm the redness and prevent it from becoming more noticeable. Avoiding excess heat and friction, hot showers, harsh scrubbing, matters too, since both aggravate the blood vessels causing the redness in the first place.
How to Treat PIH
The same 15% azelaic acid also measurably reduced pigment in PIH lesions in that same trial, so it's genuinely useful for both. If you're deciding between the OTC 10% version and a prescription, the concentration actually matters here, the trial evidence is specifically for the 15% strength. Retinoids and hydroxy acids (glycolic, lactic) help too, by speeding up cell turnover and fading pigment faster. Sun protection matters even more here than for PIE, since UV exposure directly darkens PIH and can undo months of progress in one unprotected summer.
Why Using the Wrong Treatment Can Backfire
Retinoids and other cell-turnover actives are genuinely useful for PIH, but they can irritate already-inflamed, vascular-damaged skin, which is exactly what PIE is. That irritation can prolong the redness instead of fixing it. The exact mechanism isn't fully settled, but dermatologists see this pattern often enough to plan around it. That's why figuring out which one you have comes before picking a routine, not after.
When to See a Dermatologist
- PIE that hasn't faded after several months of consistent care (vascular lasers can meaningfully speed this up)
- PIH that's stubborn or spreading despite retinoids and sun protection
- You genuinely can't tell which one you have after trying the steps above
- Marks that are raised or textured rather than flat, that's a different issue entirely, not PIE or PIH
Quick FAQ
How long does PIE take to fade on its own?
It varies widely, sometimes months, sometimes over a year. Treatment can meaningfully shorten that timeline.
Does vitamin C work on red marks?
Not particularly. Vitamin C is more useful for PIH's pigment component. For PIE, azelaic acid and niacinamide are better-supported choices.
If I have both PIE and PIH, do I need two separate routines?
Not necessarily. Azelaic acid is one of the few actives with real evidence for improving both at once, which is part of why it's worth starting there.
References
- Shucheng H, Zhou X, Du D, Li J, Yu C, Jiang X. Effects of 15% Azelaic Acid Gel in the Management of Post-Inflammatory Erythema and Post-Inflammatory Hyperpigmentation in Acne Vulgaris. Dermatology and Therapy, 2024;14:1293-1314.
- Silpa-Archa N, Kohli I, Chaowattanapanit S, Lim HW, Hamzavi I. Postinflammatory hyperpigmentation: a comprehensive overview. Journal of the American Academy of Dermatology, 2017;77(4):591-605.
- Bae-Harboe YS, Graber EM. Easy as PIE (postinflammatory erythema). Journal of Clinical and Aesthetic Dermatology, 2013;6(9):46-47.
Disclaimer: This content is for educational and informational purposes only and does not substitute for professional medical or dermatological advice. If marks are raised, textured, or spreading, consult a board-certified dermatologist. Full Medical Disclaimer.