PIE vs PIH: How to Tell Red and Brown Acne Marks Apart
Red acne marks (PIE) come from blood vessels; brown ones (PIH) come from melanin. The press test, ingredient evidence for each, timelines and sun protection.
Short answer: a red or pink mark left after a pimple is usually post-inflammatory erythema (PIE), a blood-vessel change that blanches when you press on it. A brown, gray or dark mark that does not change under pressure is post-inflammatory hyperpigmentation (PIH), extra melanin left behind by the inflammation. They respond to different things: brown marks have the deepest ingredient evidence (azelaic acid, niacinamide, daily sunscreen with visible-light protection), while red marks are vascular and have the strongest data for in-office light and laser options plus one placebo-controlled trial of prescription azelaic acid gel.
What PIE and PIH actually are
Both marks start the same way: an inflamed pimple damages the skin around it, and the skin reacts after the bump itself has gone. What differs is which part of the skin carries the leftover color.
PIE is a vascular mark. Dermatologists Yoon-Soo Bae-Harboe and Emmy Graber introduced the term in 2013 to describe the “pink-to-red discoloration after an inflammatory acne lesion,” and separated it from PIH because “PIE describes residual erythema, while PIH describes subsequent pigment change.” The color comes from small blood vessels near the surface that stay dilated, and from new vessels that formed during inflammation. A 2024 review of tranexamic acid describes post-acne erythema as possibly driven by pro-inflammatory signals and increased blood-vessel growth.
PIH is a pigment mark. Inflammation prompts pigment cells to make more melanin and hand it off to surrounding skin cells. When that extra melanin sits in the upper layer (the epidermis), the mark looks tan to dark brown. When some of it drops into the deeper layer (the dermis), the mark can look gray or blue-gray and fades more slowly. A 2010 review by Davis and Callender notes that PIH “tends to affect darker skinned patients with greater frequency and severity” and that it is among the most common reasons people with darker skin see a dermatologist.
Skin tone shapes which one you see. Bae-Harboe and Graber observed that in lighter skin (Fitzpatrick types I to III), the leftover mark is often “not hyperpigmentation, but instead discrete erythematous macules.” The authors of a 2024 azelaic acid trial summarize the same pattern: PIE predominantly affects lighter skin tones, PIH is more prevalent in darker complexions, and the two often coexist. In medium skin, a single mark often shows both.
The press test: how to check a mark in 10 seconds
Clinicians call this diascopy: pressing a clear glass slide against the skin pushes blood out of the surface vessels for a moment. Color that comes from blood inside vessels disappears; color that comes from pigment does not. You can do a home version.
- Use a clean, clear drinking glass, the flat side of a clear plastic ruler or a clear phone case.
- Press it firmly on the mark in good, natural light for 3 to 5 seconds and look through it.
- Watch the moment you lift it. A PIE mark goes pale under pressure and flushes back within a second or two. A PIH mark looks the same pressed and unpressed.
How to read mixed results. If the mark lightens but leaves a tan or brown shadow, it is both: a vascular component on top of pigment. That is common, especially in Fitzpatrick types III and IV. Handle the brown part with sun protection and pigment ingredients, and expect the red part to follow a different timeline.
A note for deeper skin tones. On deep skin, redness can look purple, dusky or dark brown, so the color alone can mislead. The press test still works because it tests where the color comes from, not what color it looks like. Gray or blue-gray marks that do not blanch suggest pigment deeper in the skin.
PIE vs PIH at a glance
| PIE (post-inflammatory erythema) | PIH (post-inflammatory hyperpigmentation) | |
|---|---|---|
| Color | Pink, red, purple-red | Tan, brown, dark brown; gray-blue when deeper |
| Source of color | Dilated and new small blood vessels | Extra melanin in the epidermis or dermis |
| Press test | Blanches, then returns | No change |
| Most common in | Lighter skin (types I to III) | Medium to deep skin (types III to VI) |
| Gets worse with | Irritation, picking, UV | UV and visible light, irritation, picking |
| Ingredients with controlled human data | 15% azelaic acid gel (prescription in the US) | Azelaic acid, niacinamide, broad-spectrum tinted sunscreen |
| In-office options | Vascular lasers (pulsed dye, Nd:YAG), intense pulsed light | Chemical peels, lasers for marks that resist topicals |
| Typical course | Fades over months; some persist | 6 to 12 months for light marks; years for deep ones (AAD) |
Why the two marks behave differently
Pigment ingredients work on the melanin pathway: they slow melanin production or block its transfer from pigment cells to skin cells. That is directly relevant to PIH. PIE has little extra melanin, so an ingredient that only works on pigment has little to act on in a pure red mark. This is the main reason people report that a brightening serum “did nothing” for their red marks.
Red marks need something that calms inflammation, reduces vessel dilation or lets the vessels remodel. Very few cosmetic ingredients have been tested that way, which is why the PIE evidence base is thinner and leans toward procedures. A 2022 systematic review of post-acne erythema screened 5,796 articles and found 18 eligible studies; light and laser devices were the most frequently studied, with pulsed dye lasers first and Nd:YAG lasers second. Topical oxymetazoline, tranexamic acid and brimonidine were described as promising, and the authors called for more randomized trials. Oxymetazoline and brimonidine are prescription vasoconstrictors in the US.
What the research says, ingredient by ingredient
| Claim | Best evidence | Study type, size, duration | Strength |
|---|---|---|---|
| Azelaic acid reduces the appearance of red acne marks | Shucheng et al. 2024, Dermatology and Therapy | Randomized, double-blind, placebo-controlled; 72 enrolled, 60 completed; 15% gel twice daily for 12 weeks; Fitzpatrick III to IV | Moderate |
| Azelaic acid reduces the appearance of brown acne marks | Same 2024 trial; Kircik 2011 pilot | 2024: PIH color and size scores better than placebo at week 12. 2011: 16-week baseline-controlled pilot of 15% gel twice daily | Moderate |
| Niacinamide reduces the appearance of hyperpigmentation | Hakozaki et al. 2002, British Journal of Dermatology | Paired vehicle-controlled trial, 18 women, 5% niacinamide moisturizer; second study of 120 women with 2% niacinamide plus sunscreen; benefit seen by week 4 | Moderate |
| Niacinamide blocks melanin transfer | Same paper, lab arm | Cell co-culture: 35% to 68% inhibition of melanosome transfer; no effect on the tyrosinase enzyme | Lab-only |
| Sunscreen reduced pigment in an induced-PIH model | Passeron et al. 2026, Dermatology and Therapy | Investigator-blinded, randomized, within-person; 20 adults, Fitzpatrick IV to V; 20 days, sunscreen vs unprotected skin after UV and visible light | Moderate |
| Visible light darkens medium and deep skin | Mahmoud et al. 2010, Journal of Investigative Dermatology | 20 volunteers, types IV to VI, compared with type II; 2-week follow-up | Moderate |
| Tranexamic acid reduces the appearance of red acne marks | Agamia et al. 2022; case report cited in Chen et al. 2024 review | Split-face, 40 patients, 3 months, 5% TXA combined with two prescription vasoconstrictors vs placebo cream; single case with 5% TXA nightly for 6 to 8 weeks | Limited |
Azelaic acid: the one ingredient with controlled data for both
The 2024 trial from West China Hospital is the clearest head-to-head data for acne marks. Sixty adults with mild to moderate acne finished 12 weeks of 15% azelaic acid gel or the same gel without azelaic acid. For red marks, the azelaic group’s median color score dropped from 6 to 3 while the placebo group stayed at 6, and the combined mark index fell from 13 to 6 versus 12 to 12 on placebo. Instrument readings showed lower hemoglobin in the red marks, which fits a vascular effect rather than simple bleaching. In the placebo group, brown marks changed only modestly (the composite index fell from a median of 12 to 9, while color and size scores did not change), whereas by week 12 the azelaic group was ahead of placebo on color and size scores, and melanin readings in its brown marks had dropped.
Two details matter for shoppers. First, 15% azelaic acid gel is a prescription product in the US (the FINACEA gel label on DailyMed is a prescription label, approved for the papules and pustules of rosacea). Second, the trial tested that gel, not a cosmetic serum. Over-the-counter products that list Azelaic Acid often do not state the percentage, and Potassium Azelaoyl Diglycinate is a different, water-soluble derivative that has not been tested in these acne-mark trials. If you pair it with niacinamide, our guide to using niacinamide and azelaic acid together covers order, pH and irritation.
Niacinamide: good data for brown, not for red
Niacinamide is one of the best-documented cosmetic ingredients for brown spots. In the 2002 Procter and Gamble study, a 5% niacinamide moisturizer reduced the appearance of facial hyperpigmentation compared with the vehicle in a paired design of 18 women, with significant change at 4 weeks. The lab work explains why: niacinamide did not slow melanin production, but it cut the transfer of pigment packets to skin cells by 35% to 68%. Those participants had general facial hyperpigmentation, not acne PIH specifically, so read it as supportive evidence for brown marks. The published controlled niacinamide data measure pigment and general blotchiness, not acne PIE, so a pure red mark is not where it shows its value.
Tranexamic acid: early evidence for red marks
Tranexamic acid is studied for both pigment and redness because it affects melanin signaling and blood-vessel growth. For acne redness specifically, the topical data are small. A 2024 review lists a single case of 5% topical tranexamic acid applied nightly for 6 to 8 weeks, and a 40-person split-face trial in which a cream combining 5% tranexamic acid with two prescription vasoconstrictors outperformed a placebo cream over 3 months. That combination design means the trial cannot isolate tranexamic acid’s share of the result. Look for Tranexamic Acid on an ingredient list if you want to try it, and expect modest change.
What about BHA and other exfoliants?
Salicylic acid and its gentler relatives keep pores clear and reduce new breakouts, and fewer new pimples means fewer new marks. That is their role here. They are not pigment or vascular ingredients. If you use a liquid exfoliant like COSRX BHA Blackhead Power Liquid, keep the frequency low enough that it never stings: Davis and Callender stress caution with every option because irritation itself can worsen PIH.
What about hydroquinone?
US readers often ask why hydroquinone creams have disappeared from drugstore shelves. Since September 23, 2020, under the CARES Act reforms, over-the-counter skin-lightening products containing hydroquinone are treated as unapproved new drugs; the FDA issued warning letters to 12 companies selling them in April 2022 and has received reports of rashes, facial swelling and ochronosis, a skin darkening that may be permanent.
Sun protection: the step that decides your timeline
For brown marks, sunscreen is not optional. Two studies explain why visible light matters as much as UV. In the 2010 Henry Ford study, visible light produced pigmentation in skin types IV to VI that was darker and longer-lasting than pigment from long-wave UVA, and produced none in type II skin. In the 2026 trial, adults with types IV to V who had small test areas irritated and then exposed to UV and visible light developed less pigment where a broad-spectrum sunscreen was applied daily for 20 days: about 16 ITA degrees of net protection on irritated skin (ITA is a colorimeter measure of skin lightness). That trial was run by the sunscreen’s maker, ISDIN, and tested a formula that also contains niacinamide and sclareolide.
The practical takeaway matches the American Academy of Dermatology’s advice for dark spots on darker skin: use a broad-spectrum, SPF 30 or higher, water-resistant sunscreen that is tinted with iron oxides, because iron oxide helps block the visible light that drives dark spots. On a US label, iron oxides appear as Iron Oxides or as CI 77491, CI 77492 and CI 77499.
For red marks, sun protection still matters. UV exposure adds its own redness and, in medium skin, tends to layer pigment on top of a PIE mark. No trial has isolated sunscreen’s effect on PIE alone, so think of it as protecting the spot from becoming a two-problem mark.
How long marks take to fade
- Light PIH: the AAD says a spot a few shades darker than your skin usually fades within 6 to 12 months.
- Deep PIH: “fading can take years,” especially gray or blue-gray marks with pigment in the dermis.
- PIE: Bae-Harboe and Graber note that both PIE and PIH tend to resolve over time, which separates them from true scars. The 40-person split-face trial of persistent post-acne erythema enrolled marks that had lasted at least 3 months, so a red mark that has lasted that long matches the marks studied in that trial.
- Any new pimple or pick in the same spot restarts the clock.
A decision path for your marks
- Are there still active pimples? Start there. New inflammation creates new marks faster than any ingredient fades old ones.
- Do the press test. Blanches means PIE; no change means PIH; partial means both.
- For brown or mixed marks: a daily tinted, broad-spectrum SPF 30+ sunscreen, plus one pigment ingredient with human data (azelaic acid or niacinamide). Give it 8 to 12 weeks before judging, which matches the trial timelines above.
- For red marks: keep the skin calm (no scrubs, no stacked acids, no hot-water face rinses), protect from sun, and consider azelaic acid. Give it 12 weeks.
- Check after 12 weeks. If a red mark has not changed, it is the type of mark the published research addresses with vascular lasers or intense pulsed light. Those are in-office options a dermatologist can discuss.
- Can you feel a dip or bump? That is a texture change, not a color mark, and topical brighteners will not change it.
Mistakes that keep marks around longer
- Using a pigment-only routine on red marks and concluding nothing works.
- Over-exfoliating. Stinging, peeling and redness from too many actives add inflammation, and inflammation is what made the mark.
- Skipping sunscreen on cloudy or indoor days. Visible light passes through ordinary window glass, and untinted sunscreens block little of it.
- Picking or squeezing. Each one deepens the damage that leaves the mark.
- Buying imported lightening creams with unclear labels. The AAD warns that some contain unlisted steroids or mercury.
A board-certified dermatologist can help when marks persist for many months, when you see indented or raised scarring, or when you are unsure whether a mark is from acne at all.
Related reading
- Why is my vitamin C serum turning orange? for keeping a brightening serum effective.
- Can you use niacinamide and azelaic acid together?
- COSRX BHA Blackhead Power Liquid: what the formula does
Sources and research notes
Peer-reviewed studies and reviews on post-inflammatory erythema and hyperpigmentation after acne, including a placebo-controlled azelaic acid trial, niacinamide, tranexamic acid and visible-light sunscreen studies, plus AAD guidance, the FDA notice on OTC hydroquinone and the DailyMed azelaic acid gel label, checked on the date shown.
Source record date: 2026-10-06. Prices and availability are as of that date.
- Bae-Harboe YS, Graber EM. Easy as PIE (Postinflammatory Erythema). J Clin Aesthet Dermatol, 2013
- Shucheng H et al. 15% azelaic acid gel for acne PIE and PIH: randomized, double-blind, placebo-controlled trial (n=72, 12 weeks). Dermatol Ther, 2024
- Kalantari Y et al. Post-acne erythema treatment: a systematic review. J Cosmet Dermatol, 2022
- Davis EC, Callender VD. Postinflammatory hyperpigmentation in skin of color: review. J Clin Aesthet Dermatol, 2010
- Hakozaki T et al. Niacinamide reduces cutaneous pigmentation and melanosome transfer. Br J Dermatol, 2002
- Kircik LH. Azelaic acid gel 15% for post-inflammatory hyperpigmentation and acne: 16-week pilot. J Drugs Dermatol, 2011
- Mahmoud BH et al. Long-wavelength UVA and visible light on melanocompetent skin. J Invest Dermatol, 2010
- Passeron T et al. Randomized trial of a broad-spectrum sunscreen for PIH prevention in skin of color. Dermatol Ther, 2026
- Agamia N et al. Split-face trial of a topical triple combination for persistent post-acne erythema. Dermatol Ther, 2022
- Chen T et al. Tranexamic acid for hyperpigmentation and telangiectatic disorders other than melasma: an update. Clin Cosmet Investig Dermatol, 2024
- American Academy of Dermatology: How to fade dark spots in darker skin tones
- US FDA: FDA works to protect consumers from potentially harmful OTC skin lightening products
- DailyMed: FINACEA (azelaic acid) gel 15% prescription label
Frequently asked questions
How can I tell if my acne mark is PIE or PIH at home?
Press a clear glass or a clear plastic ruler firmly on the mark for a few seconds and look through it. If the mark fades or turns pale under pressure and the color returns when you lift it, the color is coming from blood in dilated vessels (PIE). If the color stays the same, it is pigment (PIH). Many marks are a mix of both.
Does niacinamide help red acne marks?
Niacinamide's controlled data cover brown spots and general red blotchiness in aging skin, not acne PIE specifically. In a paired, vehicle-controlled study of 18 Japanese women, a 5% niacinamide moisturizer reduced the appearance of hyperpigmentation within 4 weeks. For red marks, the strongest controlled data in this guide are for 15% azelaic acid gel, which is a prescription product in the US.
How long do brown acne marks take to fade?
The American Academy of Dermatology says a spot a few shades darker than your natural skin tone usually fades within 6 to 12 months, while deeper discoloration can take years. Daily sun protection, including protection from visible light, keeps that clock from resetting.
Do I need sunscreen for red acne marks too?
Yes, though the reason is different. Sunscreen has direct evidence for preventing brown marks from darkening. For red marks, sunscreen limits the extra UV redness and the new pigment that can build up in the same spot, so the mark does not become a red-plus-brown mark.
Are acne marks the same as acne scars?
No. PIE and PIH are flat color changes that tend to fade with time. Scars change the skin surface: they are pitted, indented or raised. A mark you can feel as a dip or bump when you run a finger across it is a texture change rather than a color change.