Post-Inflammatory Hyperpigmentation (PIH): A Clear Guide

What Is Post-Inflammatory Hyperpigmentation?

Post-inflammatory hyperpigmentation (PIH) is the flat, dark or discolored mark left at the site of healed skin inflammation. It is not a scar — there is no change to the skin's collagen structure or surface texture. PIH is purely a pigmentation change: excess melanin deposited at the site during and after the inflammatory process.

PIH can result from virtually any type of skin inflammation or injury:

• Acne — the most common cause in most skin types
• Eczema (atopic dermatitis)
• Psoriasis
• Contact dermatitis
• Insect bites
• Burns
• Cuts and abrasions
• Cosmetic procedures — chemical peels, laser resurfacing, dermabrasion, waxing
• Ingrown hairs

The resulting marks are typically tan, brown, dark brown, or reddish-brown in lighter skin tones, and dark brown to near-black or ashen gray in deeper skin tones, reflecting the deeper deposition of melanin in more melanin-rich skin.

PIH is extremely common. Surveys show it affects over 65% of patients with acne globally, with rates rising substantially in patients with Fitzpatrick skin types IV–VI. In clinical surveys of patients of African and Asian descent presenting to dermatologists, PIH is frequently cited as the primary concern — more distressing than the underlying inflammatory condition that caused it.

Why Darker Skin Tones Are Disproportionately Affected

Understanding this disproportion requires a brief explanation of melanin biology:

Melanocyte density is similar across skin tones. What differs is melanocyte activity and distribution of melanosomes (the organelles that package and transport melanin). In Fitzpatrick types V–VI, melanocytes are more reactive — they produce more melanin in response to inflammation, and the melanin produced is packaged in larger, individually distributed melanosomes that are more photostable (slow to degrade).

Epidermal vs. dermal PIH: When inflammation is mild, melanin deposits primarily in the epidermis (the outer skin layers), producing a tan to brown mark that fades relatively predictably with topical treatment and time. When inflammation is significant or the skin type is darker, melanin-laden melanocytes and macrophages (melanophages) can deposit pigment into the dermis — the deeper layer. Dermal melanin appears gray, blue-gray, or grayish-brown and is much more difficult to treat topically because most topical brighteners do not penetrate deeply enough to target it effectively.

This is why the same pimple can leave a barely visible mark in fair skin and a deep, long-lasting mark in brown or dark skin — and why treatment must be proportionate to the skin tone and the depth of PIH.

Distinguishing PIH from Acne Scars

PIH is frequently confused with acne scarring, but they are fundamentally different and require different management:

A patient can have both PIH and atrophic scarring from the same acne lesion — the flat dark marks respond to brightening treatment while the depressed pits do not.

Step 1: Treat the Underlying Inflammatory Cause

The most important and most frequently overlooked step in PIH management is controlling the source of inflammation. Every new acne papule, eczema flare, or scratched insect bite has the potential to create a new PIH mark. Until the inflammatory condition is controlled, the problem is being continuously renewed from the source.

For PIH from acne: effective acne treatment (OTC adapalene, benzoyl peroxide, salicylic acid; prescription retinoids or antibiotics for moderate-severe cases) reduces the formation of new lesions and therefore prevents new PIH while existing marks fade.

For PIH from eczema or psoriasis: working with a dermatologist to achieve better disease control — through topical corticosteroids, calcineurin inhibitors, biologics, or phototherapy as appropriate — is essential before the PIH can meaningfully resolve.

The Treatment Approach

Non-Negotiable: Daily SPF 50+

UV exposure stimulates melanocytes throughout the skin, but the melanocytes at a PIH site are already in a hyperactivated state — they are significantly more responsive to UV than surrounding normal skin. Even modest UV exposure darkens existing PIH marks and slows or reverses fading. Daily, year-round broad-spectrum SPF 50+ is the most important treatment step — not a supplement to brightening actives but the prerequisite that enables them.

Evidence-Based Topical Brighteners for PIH

Azelaic acid (10–20%): A dicarboxylic acid that selectively inhibits hyperactive melanocytes at PIH sites without significantly affecting normally active melanocytes. This selective action is particularly valuable for PIH treatment compared to hydroquinone, which inhibits melanin production broadly. Azelaic acid also has clinically proven anti-inflammatory properties, making it doubly useful when PIH is caused by ongoing acne or rosacea. It is safe in pregnancy (category B) and well tolerated across all Fitzpatrick skin types. The 20% prescription formulation provides faster results; 10% OTC is effective but takes longer.

Niacinamide (5–10%): Inhibits the transfer of melanosomes from melanocytes to keratinocytes — a different mechanism to tyrosinase inhibitors. Multiple clinical trials confirm visible brightening over 8–12 weeks. Exceptionally well tolerated, no irritation risk, safe in pregnancy, and appropriate for all skin tones including Fitzpatrick VI. Can be applied morning and evening.

Retinoids (retinol OTC; tretinoin Rx): Retinoids accelerate keratinocyte turnover, reducing the residence time of melanin-containing cells at the skin surface and accelerating their shedding. They also inhibit tyrosinase and reduce melanosome transfer. Prescription tretinoin (0.025–0.05%) produces faster results than OTC retinol for PIH, but the initial retinization/purge period (dryness, flaking, and occasionally increased breakouts) must be managed carefully in darker skin tones to avoid barrier disruption that could itself trigger more PIH. Start low, go slow: 0.025–0.1% retinol twice weekly, building frequency over 8–12 weeks. Use with nightly moisturizer.

Vitamin C (L-ascorbic acid, 15–20%): Inhibits tyrosinase, neutralizes UV-generated reactive oxygen species, and provides antioxidant protection when applied in the morning before SPF. Most effective as a daytime antioxidant supporting the photoprotection strategy. Less potent as a standalone brightener than azelaic acid or hydroquinone, but a clinically useful addition to a complete regimen.

Tranexamic acid (topical 2–5%): Disrupts keratinocyte-melanocyte signaling via the plasminogen-dependent pathway. Growing evidence supports use for PIH, particularly in combination products. Well tolerated.

Hydroquinone (2–4% OTC/Rx): The most potent single topical brightener; inhibits tyrosinase and impairs melanosome synthesis. Effective but should be used in 3–4 month cycles to avoid exogenous ochronosis — a paradoxical permanent blue-black pigmentation that occurs with prolonged uninterrupted use, with higher risk in darker skin tones. Not recommended during pregnancy. For severe PIH in deeper skin tones, prescription 4% hydroquinone under dermatologist guidance offers the fastest topical results.

Kojic acid (1–4%) and alpha-arbutin (1–2%): Both inhibit tyrosinase. Well-evidenced adjuncts to a complete regimen. Kojic acid can cause contact sensitization with long-term use; kojic dipalmitate formulations are more stable. Alpha-arbutin is generally better tolerated than kojic acid with comparable efficacy.

Putting It Together: Sample Regimens

OTC regimen for mild-moderate PIH (all skin tones)

Morning:

• Gentle cleanser
• Vitamin C serum (15–20% L-ascorbic acid)
• Niacinamide moisturizer (5–10%)
• SPF 50+ (tinted mineral if darker skin tone)

Evening:

• Double cleanse
• Azelaic acid (10% OTC) or niacinamide treatment
• 2–4 nights per week: retinol (0.1–0.3%, building to 0.5%)
• Moisturizer (ceramide-based)

Expected timeline: First visible improvement 8–12 weeks; significant improvement 3–6 months for epidermal PIH.

Prescription regimen for moderate-severe PIH (dermatologist supervised)

Morning:

• Gentle cleanser
• Vitamin C serum
• Moisturizer
• SPF 50+ tinted mineral

Evening:

• Azelaic acid 20% (or hydroquinone 4% in treatment cycles)
• Tretinoin 0.025–0.05% (2–3× weekly, building to nightly over 8 weeks)
• Ceramide moisturizer

Expected timeline: Visible improvement 4–8 weeks; significant improvement 3–4 months. Dermal PIH may take 12+ months.

Professional Procedures for Resistant PIH

For deep dermal PIH that is not responding to topicals after 3–6 months:

Chemical peels: Superficial peels (glycolic acid 20–35%, salicylic acid 20–30%, or Jessner's formula) accelerate epidermal turnover. In Fitzpatrick types IV–VI, superficial peels are preferred — medium-depth peels carry high PIH risk in darker skin. Pre-conditioning with topical depigmenting agents for 4–6 weeks before peeling significantly reduces post-peel PIH risk. Series of 4–6 peels, 3–4 weeks apart.

Q-switched Nd:YAG 1064 nm laser: The longest-wavelength Q-switched laser passes more deeply into the dermis with less epidermal absorption — the safest profile for targeting pigment in darker skin. Multiple sessions required. Risk of post-procedural PIH exists even with this wavelength; strict post-procedure SPF and topical preconditioning reduce but do not eliminate the risk.

Microneedling: Increasing evidence for dermal PIH; may improve pigment that topicals cannot reach. Enhanced penetration of topical brighteners when applied immediately after microneedling.

What Not to Do

• Pick, squeeze, or pop pimples. The additional trauma directly deepens and expands PIH at the site — a brief moment of pressure creates a mark that takes months to fade.
• Aggressive physical exfoliation. Harsh scrubs create micro-trauma and inflammation that can produce new PIH.
• Skip sunscreen. The single most common reason PIH does not improve despite treatment is ongoing UV re-stimulation of hyperactive melanocytes.
• Overdo actives. Irritating the skin with too many actives at once disrupts the barrier and can trigger inflammation that creates new PIH in sensitive skin — a particularly significant risk in darker skin tones.

Frequently Misunderstood: PIH vs. Erythema

Fresh acne marks in lighter skin tones are often pink or red initially before becoming brown. This early pink or red appearance is post-inflammatory erythema (PIE) — dilated blood vessels left by inflammation, not excess melanin. PIE requires a different approach (azelaic acid helps with both; niacinamide helps; vascular lasers like pulsed-dye laser are specifically effective for PIE). It is worth knowing which you have — a dermatologist can tell on examination.