Data guide / Concern guide
The best ingredients for acne marks (PIH vs PIE)
First identify the mark: flat BROWN marks (PIH) are excess pigment and respond to azelaic acid, niacinamide, vitamin C, and exfoliating acids; flat RED/pink marks (PIE) are dilated vessels and respond better to barrier repair, anti-inflammatory care, and tranexamic acid. Azelaic acid is the most versatile single pick, and SPF is mandatory for both.
know which mark you have
PIH vs PIE
After a pimple heals it often leaves a flat mark — and which one you have decides what to use. Post-inflammatory hyperpigmentation (PIH) is a flat BROWN or tan spot caused by excess melanin from the inflammation; it responds to pigment-fading actives and faster cell turnover. Post-inflammatory erythema (PIE) is a flat PINK or red mark caused by damaged, dilated capillaries; it does not respond to brighteners and instead needs barrier repair, gentle anti-inflammatory care, time, and — for the vascular component — tranexamic acid. A quick test: press the mark; if it briefly blanches (goes pale) it is likely PIE (vascular); if the colour stays it is likely PIH (pigment). Azelaic acid is the most useful single ingredient because it helps both. Two rules apply to either: protect with daily broad-spectrum SPF (UV darkens marks and slows fading), and stop picking — fresh inflammation makes new marks faster than any active fades the old ones. Expect 8–12 weeks, longer for deep marks; truly stubborn PIE may need in-office laser treatment.
Azelaic Acid dossier ↗ · Niacinamide (Vitamin B3) dossier ↗ · L-Ascorbic Acid (Vitamin C) dossier ↗ · Tranexamic Acid dossier ↗ · Glycolic Acid (AHA) dossier ↗
02 / Azelaic acid
Azelaic acid: the acne-marks all-rounder
Azelaic acid is the single best pick for post-acne marks because it works on three fronts at once: it competitively inhibits tyrosinase and selectively targets the overactive melanocytes that create brown PIH, it is anti-inflammatory (it scavenges the free radicals neutrophils release during a breakout), and it treats the acne lesions that cause the marks. That anti-inflammatory action also helps the red PIE side, making it the most versatile choice for blemish-prone skin.
- Study Azelaic acid competitively inhibits tyrosinase activity and selectively inhibits hyperactive melanocyte proliferation and DNA synthesis without significantly affecting normal melanocytes, reducing the risk of hypopigmentation in adjacent healthy skin. 1
- Study Azelaic acid markedly decreases superoxide (O2-) and hydroxyl radical (OH.) generated by neutrophils, reducing oxidative tissue injury at inflammatory sites and contributing to melanin reduction. 2
03 / Niacinamide
Niacinamide: gentle, helps both brown and red marks
Niacinamide is the easy add-on for either mark type. For brown PIH it blocks the transfer of finished melanin from pigment cells to the surface, and for red PIE it rebuilds the skin barrier — it raises ceramide production several-fold — which calms the low-grade inflammation and supports the vessels that keep PIE looking pink. It is well tolerated and layers with everything.
- Study Niacinamide inhibits melanosome transfer from melanocytes to adjacent keratinocytes by 35–68% in co-culture models; it does not inhibit tyrosinase activity or melanin synthesis in melanocytes — the mechanism is specific to the transfer step. 3
- Study Nicotinamide increases ceramide biosynthesis dose-dependently (4.1–5.5-fold at 1–30 μmol/L over 6 days), increases glucosylceramide (7.4-fold) and sphingomyelin (3.1-fold) synthesis, and upregulates serine palmitoyltransferase — the rate-limiting enzyme in sphingolipid synthesis — in cultured human keratinocytes; topical application also increased ceramide levels in the stratum corneum and reduced transepidermal water loss. 4
04 / Vitamin C
Vitamin C: fades pigment and supports repair
L-ascorbic acid earns its place for acne marks two ways: it inhibits tyrosinase to lighten brown PIH, and as a cofactor for collagen-building enzymes it supports the skin repair that healing marked skin needs. Its antioxidant action also buffers the daily UV that deepens any mark. A reliable morning base under sunscreen.
- Study Inhibits melanin synthesis by reducing tyrosinase enzyme activity and reducing melanin formation in melanoma cells in vitro. 5
- Review Acts as a cofactor for prolyl and lysyl hydroxylases, enabling hydroxylation of proline and lysine residues in procollagen, which is required for stable triple-helix collagen formation. 6
05 / Tranexamic acid
Tranexamic acid: for the red, vascular marks (PIE)
PIE — the flat pink-to-red marks left after a breakout — is a vascular problem, not a pigment one, which is why pure brighteners disappoint on it. Tranexamic acid is the most relevant active here because it damps the VEGF-driven angiogenesis behind that redness, and it has melasma trial support for stubborn discoloration generally. It is a targeted choice when your marks are red rather than brown.
- Study A topical depigmentation formulation containing tranexamic acid reduced VEGF and iNOS protein synthesis in cultured dermal fibroblasts under UV stress, indicating an anti-angiogenic property; it also decreased endothelin-1, PAR-2, and tyrosinase activity. 7
- Study A systematic review and meta-analysis of 11 studies (667 participants) found that tranexamic acid monotherapy produced a pooled MASI decrease of 1.60 points (95% CI 1.20-2.00; p<0.001); as an adjuvant it added an additional reduction of 0.94 points (p=0.03). 8
06 / Glycolic acid (AHA)
Glycolic acid: speed up turnover for brown marks
For brown PIH, exfoliating acids accelerate the fade by clearing pigmented dead cells and raising skin turnover — glycolic is the classic alpha-hydroxy acid exfoliant, documented to work on the epidermis to renew the surface. Use it for the brown marks, not the red ones, and never without daily sunscreen, since AHAs increase sun sensitivity.
- Study Alpha-hydroxy acids, including glycolic acid, were first documented as therapeutic exfoliants for ichthyotic (hyperkeratotic) skin disorders; Van Scott and Yu's 1974 seminal paper established AHAs as agents capable of controlling keratinization. 9
- Study Application of 25% glycolic, lactic, or citric acid lotion to forearms for approximately 6 months produced an approximately 25% increase in skin thickness, with increased acid mucopolysaccharides, improved elastic fiber quality, and increased collagen density in the dermis — significant reversal of epidermal and dermal markers of photoaging — without an inflammatory response. 10
07 / Summary
Key takeaways
- Identify the mark first: brown = PIH (pigment), red/pink = PIE (vascular). The blanch test (press it) helps.
- Azelaic acid is the best single pick — it fades PIH, calms inflammation, and treats the acne itself.
- PIE responds to barrier repair (niacinamide), anti-inflammatory care, and tranexamic acid — not to brighteners.
- Daily SPF is mandatory, and not picking is half the battle — new inflammation makes new marks.
- Give it 8–12 weeks; stubborn red marks (PIE) may ultimately need in-office laser treatment.
08 / Questions
Frequently asked
- What is the difference between PIH and PIE acne marks?
- PIH (post-inflammatory hyperpigmentation) is a flat brown or tan mark from excess melanin produced during the inflammation of a breakout — it is a pigment problem. PIE (post-inflammatory erythema) is a flat pink or red mark from dilated, damaged capillaries — it is a vascular problem. They respond to different ingredients, so identifying which you have matters. A rough test: press the mark; PIE tends to blanch (go pale) briefly, PIH stays the same colour. 17
- What is the best ingredient for brown acne marks (PIH)?
- Azelaic acid is the most versatile choice — it inhibits tyrosinase, selectively targets the overactive pigment cells, and treats the acne itself. Niacinamide and vitamin C are gentle supporting brighteners, and glycolic acid — the classic AHA exfoliant — speeds the fade by accelerating surface turnover. All require daily SPF. 19
- What helps red acne marks (PIE)?
- Because PIE is vascular, brighteners don't help much. Focus on barrier repair and anti-inflammatory care — niacinamide rebuilds ceramides and calms the skin, azelaic acid reduces inflammation, and tranexamic acid targets the VEGF-driven blood-vessel component behind the redness. Time and rigorous sun protection do a lot of the work, and persistent PIE may need vascular laser treatment. 47
- How long do acne marks take to fade?
- Most flat marks fade over 8–12 weeks with consistent treatment, and deeper or older marks take longer. Two things speed it up the most and cost nothing: daily broad-spectrum sunscreen (UV deepens marks and stalls fading) and not picking at spots, since each new bout of inflammation creates fresh marks. If a mark is raised or indented rather than flat, that is scarring, not PIH/PIE, and needs different, often in-office, treatment. 96
09 / References
Sources
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