One of the most frustrating parts of dealing with acne is what gets left behind after a pimple finally heals. Those lingering red or brown spots can sometimes feel more persistent than the breakout itself. Many people group all post-acne marks under the general term “acne scars,” but in reality, there are two common types of flat discoloration that are not true textural scars: Post-Inflammatory Erythema (PIE) and Post-Inflammatory Hyperpigmentation (PIH).
Understanding the crucial difference between these two is the single most important step in effectively treating them. They have different causes and therefore respond to completely different treatments. Using the wrong approach can waste time, money, and even worsen the condition. This guide will help you differentiate between PIE and PIH and understand the best ways to treat each.
Important Disclaimer: This article is for educational purposes. For an accurate diagnosis and personalized treatment plan, it’s essential to consult a board-certified dermatologist.
What is Post-Inflammatory Erythema (PIE)? (The Red/Pink Spots)
Post-Inflammatory Erythema (PIE) is the name for the persistent flat red, pink, or purplish spots left behind after an inflammatory event, most commonly an acne lesion.
- The Cause: PIE is a vascular issue. The inflammation from the acne pimple causes damage to or dilation of the tiny blood vessels (capillaries) near the skin’s surface. The red or pink color is the visible result of these damaged capillaries. It is not a problem of skin pigment.
- Appearance: Flat red, pink, or purple macules (spots).
- How to Test for it (The Blanching Test): A simple way to identify PIE is to apply gentle pressure to the spot with a clear object (like a glass slide or a clear glass cup). If the redness temporarily disappears or “blanches” (turns white) and then returns when pressure is released, it is very likely PIE. This is because you are momentarily pushing the blood out of the dilated vessels.
- Common in: While it can occur in all skin tones, PIE is often more noticeable and common in individuals with lighter skin tones (Fitzpatrick types I-III).
What is Post-Inflammatory Hyperpigmentation (PIH)? (The Brown/Black Spots)
Post-Inflammatory Hyperpigmentation (PIH) is the name for the flat brown, black, or greyish spots that remain after skin inflammation.
- The Cause: PIH is a pigment issue. The inflammation triggers an overproduction of melanin (the pigment that gives skin its color) by your pigment-producing cells (melanocytes). This excess melanin gets deposited in the skin, creating a dark spot.
- Appearance: Flat brown, black, or dark grey spots.
- How to Test for it: Unlike PIE, PIH will not blanch or change color when pressure is applied, because the discoloration is due to pigment deposited in the skin, not blood in vessels.
- Common in: While it can affect anyone, PIH is more common and often more persistent in individuals with medium to darker skin tones (Fitzpatrick types IV-VI), as their skin naturally produces more melanin. This is a very common concern in diverse regions like Indonesia.
PIE vs. PIH: Key Differences Summarized
| Feature | PIE (Post-Inflammatory Erythema) | PIH (Post-Inflammatory Hyperpigmentation) |
|---|---|---|
| Primary Color | Red, Pink, Purple | Brown, Black, Grey |
| Underlying Cause | Damaged/Dilated Blood Vessels (Vascular) | Overproduction of Melanin (Pigment) |
| Blanching Test? | Yes (Spot turns white under pressure) | No (Spot does not change color under pressure) |
| Most Common In | Lighter Skin Tones | Medium to Darker Skin Tones |
| Primary Treatment Focus | Calming inflammation, repairing the skin barrier, and targeting blood vessels. | Inhibiting melanin production and increasing skin cell turnover. |
It’s possible to have both PIE and PIH present on the skin at the same time.
Treatment Strategies for PIE (The Red Marks)
Because PIE is a vascular issue, treatment focuses on calming inflammation, supporting healing, and targeting redness.
Essential First Steps (For Everyone):
- Patience and Time: PIE can often fade on its own, but it can take many months (6-12 months or longer).
- SUNSCREEN, SUNSCREEN, SUNSCREEN: This is non-negotiable. UV exposure can worsen inflammation and prolong the redness. Daily use of a broad-spectrum SPF 30+ sunscreen is crucial to allow the skin to heal properly.
Effective Topical Ingredients for PIE:
- Niacinamide (Vitamin B3): An excellent ingredient for PIE due to its strong anti-inflammatory properties and its ability to support and strengthen the skin barrier.
- Azelaic Acid: Helps to reduce inflammation and redness. It also has mild benefits for pigmentation, making it useful if you have both PIE and PIH.
- Vitamin C (Ascorbic Acid & Derivatives): A potent antioxidant that can help reduce inflammation and support collagen production for overall skin health.
- Soothing & Barrier-Supporting Ingredients: Look for products containing Centella Asiatica (Cica), Green Tea Extract, Ceramides, and Panthenol to help calm the skin and repair its protective barrier.
Professional Treatments for PIE:
For persistent or widespread PIE, in-office treatments are most effective:
- Vascular Lasers (Gold Standard): Lasers like Pulsed Dye Laser (PDL) and Intense Pulsed Light (IPL) specifically target the red pigment (hemoglobin) in blood vessels, reducing redness and helping to clear the marks effectively. Multiple sessions are usually required.
- Microneedling: Can help remodel the skin and stimulate collagen, which may indirectly improve the appearance of PIE over time, but lasers are generally more direct for this concern.
Treatment Strategies for PIH (The Brown Marks)
Because PIH is a pigment issue, treatment focuses on inhibiting melanin production and increasing skin cell turnover to shed the pigmented cells.
Essential First Step (Again):
- SUNSCREEN IS CRITICAL: Sun exposure is the primary factor that makes dark spots darker and more stubborn. Daily, diligent use of broad-spectrum SPF 30+ is the most important part of any PIH treatment plan.
Effective Topical Ingredients for PIH:
- Topical Retinoids: (e.g., Prescription Tretinoin, or OTC Adapalene and Retinol). These Vitamin A derivatives are highly effective as they increase skin cell turnover, helping to exfoliate pigmented cells more quickly.
- Tyrosinase Inhibitors (Pigment Blockers): These ingredients work by blocking the enzyme responsible for producing melanin. Examples include:
- Hydroquinone: (Prescription-strength is most effective, use only under dermatologist supervision due to potential side effects).
- Azelaic Acid: A standout ingredient that both inhibits pigment and reduces inflammation.
- Tranexamic Acid, Kojic Acid, Alpha Arbutin, Licorice Root Extract.
- Vitamin C: Helps inhibit melanin production and brighten the skin.
- Exfoliating Acids (AHAs): Ingredients like Glycolic Acid help to exfoliate the surface of the skin, speeding up the removal of darkened cells.
Professional Treatments for PIH:
- Chemical Peels: Superficial peels containing Glycolic Acid or similar acids, performed in a series, are very effective for lifting hyperpigmentation.
- Laser Treatments: Pigment-targeting lasers like Q-switched lasers and Picosecond lasers can break up excess melanin in the skin. These must be used with great care on darker skin tones to avoid worsening pigmentation.
Prevention is Always the Best Approach
The best way to deal with PIE and PIH is to prevent them from forming in the first place:
- Treat Acne Effectively and Early: The less inflammation you have, the lower the risk of developing these marks.
- DO NOT PICK, POP, or SQUEEZE PIMPLES: This causes significant trauma and inflammation, which is the direct cause of both PIE and PIH.
- Use a Gentle Skincare Routine: Avoid harsh scrubs and irritating products that can compromise your skin barrier.
- Wear Sunscreen Daily: Protects healing skin and prevents existing marks from worsening.
Conclusion
The lingering spots after an acne breakout can be either red/pink (PIE, a vascular issue) or brown/dark (PIH, a pigment issue), and knowing the difference is crucial for effective treatment. You can identify PIE with the “blanching test.” While both conditions benefit greatly from daily sunscreen use and not picking acne, their core treatments diverge. PIE responds best to anti-inflammatory topicals and vascular lasers, while PIH is treated with pigment inhibitors, retinoids, and exfoliating peels. If you are struggling with persistent post-acne marks, a consultation with a board-certified dermatologist can provide an accurate diagnosis and a targeted treatment plan to help you achieve a clearer, more even complexion.