Post-Inflammatory Hyperpigmentation: Why Skin Darkens After Treatment

When skin is inflamed (burns, acne, energy-based treatment, trauma), inflammatory mediators (prostaglandins, leukotrienes, endothelin) push melanocytes into overdrive. Some melanin drops into the dermis and is retained by melanophages — the epidermal part fades in months, the dermal part can persist 6-12+ months.

• Fitzpatrick III-VI: inherently active melanocytes.
• Melasma-prone skin: any stimulus can trigger it.
• Over-fluenced treatments: burn-grade inflammation.
• No sun protection / picking crusts after treatment.

Darkening peaks 2-4 weeks post-treatment, then fades monthly: epidermal type 3-6 months, dermal type 6-18. “It looked darker right after” is not failure — assess on the timeline.

1. Strict photoprotection: physical shading first; reapply sunscreen every 2-3 hours.
2. Topicals: retinoids, niacinamide, tranexamic acid per physician guidance.
3. Device adjunct: low-fluence picosecond or large-spot 1064 (after inflammation fully subsides).
4. Oral: tranexamic acid under physician assessment.

In practices with many darker-skin clients, put “PIH informed consent + follow-up photos” into the SOP — most complaints are expectation mismatch, not true error. Fine-stepped, stable, well-cooled platforms (LEIJEX picosecond and OPT lines) materially reduce PIH rates.

Continue treatment while PIH is present?

Fade first: stacking energy on active inflammation deepens PIH. Restart 1-3 months later at lower fluence once pigment clearly fades.

PIH or melasma?

PIH has a triggering event and matches the original injury’s shape; melasma is symmetric, diffuse and slow. Wood’s lamp helps localize depth.

• Melasma
• Melanogenesis
• Freckles and Lentigines