What Works Skin — Independent · Evidence-First · Ad-FreeIssue 014 · 20 April 2026 · Next: 04 Maywhatworksskin.com
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Concern · Pigmentation · PIH

P. 22 · GUIDE

The brown shadow
acne leaves behind.

Acne and injury aftermath. Faster to fade than melasma.

The flat, brown-to-violaceous patches that linger for months after a pimple resolves. More common, more persistent, and more under-treated in melanin-rich skin than the pigmentary concerns that get the airtime.

— § 01

The triggers worth tracking.

Brown / dark patches at sites of past acne

Flat, sharply circumscribed. Not raised, not pink. The marker that tells you it is PIH and not active inflammation.

94%
Persists 3–18 months without active treatment

Spontaneous resolution is real but slow. Treatment compresses the timeline by months.

82%
Worsens with sun exposure even briefly

UV is the single biggest accelerant. Daily SPF is the most consequential variable in any PIH protocol.

88%
Triggered by friction, picking, or BPO sting

The inflammation does not need to be acne-shaped. Any trauma can produce a PIH plaque.

71%
⁂

— § 02

Ingredients that actually work.

Tier
Molecule
Role
Evidence
Tier A
Azelaic acid 10–15%
Tyrosinase inhibitor
First-line, pregnancy-safe, replicated 12-week PIH endpoints across skin types.
Tier A
Tranexamic 5% topical
Plasmin inhibitor
Replicated efficacy in skin of colour at 8–12 weeks. Pairs cleanly with azelaic.
Tier A
Niacinamide 4–10%
Melanosome transfer
Slows pigment hand-off from melanocyte to keratinocyte. Strong barrier credentials.
Tier B
Alpha arbutin 2%
Tyrosinase inhibitor
Gentler than hydroquinone, slower endpoints. Safe in pregnancy.
Tier B
Cysteamine 5%
Antioxidant pigment-blocker
Promising in stubborn PIH; short contact protocol; smell remains the limiter.
Tier A
Hydroquinone 4%
Tyrosinase inhibitor
Reference compound. Cycle 3 months on, 2 off. Not in pregnancy.
⁂

— § 03

The protocol.

  1. Phase 01 · Week 1–4

    SPF + barrier

    Mineral SPF 50+ daily, two finger-lengths. Ceramide moisturiser. No active layering yet — establish UV discipline first.

  2. Phase 02 · Week 4–8

    Add azelaic

    Azelaic 10% PM, build to nightly. Continue niacinamide AM. The 8-week mark is the earliest reasonable photo check.

  3. Phase 03 · Week 8–16

    Layer tranexamic

    Tranexamic 5% AM under SPF. Optional cysteamine introduction at week 12 if response plateaus.

  4. Phase 04 · Month 4+

    Maintenance

    Continue SPF and azelaic indefinitely; cycle hydroquinone or cysteamine in 3-month windows. Re-photograph every 8 weeks.

Bottom line

The condition with the highest treatment-discipline payoff in pigmentation. Most failed cases are sun-discipline failures, not molecule failures. Photograph at month 0 and month 4 — you will not believe the change otherwise.