What is the recommended treatment protocol for post-inflammatory hyperpigmentation (PIH) after injections in a patient with a history of injections, considering their skin type and tone?

Treatment Protocol for Post-Inflammatory Hyperpigmentation After Injections

For post-inflammatory hyperpigmentation (PIH) following injections, initiate treatment with a topical retinoid combined with hydroquinone 4% and strict photoprotection using broad-spectrum SPF 30 or greater sunscreen, as this combination approach demonstrates the highest rates of partial response (72-85%) compared to monotherapy. 1, 2

Initial Management Strategy

Address Ongoing Inflammation First

• Recognize that subtle ongoing inflammation may persist, especially in darker skin phenotypes (Fitzpatrick IV-VI), and must be controlled before initiating depigmentation therapy 1
• Consider low-to-moderate potency topical corticosteroids if residual inflammation is present at injection sites, though use judiciously to avoid additional pigmentary changes 3, 4

First-Line Topical Therapy

Start with combination topical therapy rather than monotherapy:

• Hydroquinone 4% as the primary depigmenting agent, applied twice daily to affected areas 5, 1, 6
• Topical retinoids (tretinoin, adapalene, or tazarotene) to enhance epidermal turnover and pigment dispersion 3, 1, 7
• Azelaic acid as an alternative or adjunctive tyrosinase inhibitor if hydroquinone is not tolerated 3, 6

Mandatory Photoprotection

• Apply broad-spectrum sunscreen with SPF 30 or greater daily, as even minimal sunlight sustains melanocytic activity and prevents repigmentation 5, 1
• This is essential during treatment and maintenance therapy 5
• Recommend physical sun avoidance and protective clothing for injection sites on exposed areas 5

Treatment Algorithm by Response

For Partial Response at 8-12 Weeks (Expected in 72-85% of Cases)

• Continue current regimen if improvement is noted 2
• Consider adding niacinamide or thiamidol as adjunctive agents, which have high-quality evidence for PIH 1
• Incorporate hydroxy acids (glycolic or salicylic acid) for enhanced exfoliation 1

For Poor or No Response at 12 Weeks (Occurs in 22% of Cases)

• Transition to fixed-dose triple combination: fluocinolone acetonide 0.01% + hydroquinone 4% + tretinoin 0.05% 7
• Alternative: mequinol 2% + tretinoin 0.01% solution, which shows promise for recalcitrant PIH 7
• Consider referral for procedural interventions if topical therapy fails 2, 8

For Recalcitrant Cases

• Combination therapy with topicals plus procedures yields 84.9% partial response rates 2
• Laser and energy-based devices achieve complete resolution in 18-26% of cases but carry risk of PIH worsening (2.6% of patients) 2, 8
• Chemical peels show lower efficacy (33.3% partial response) and higher failure rates (66.7% poor/no response) 2

Critical Considerations by Skin Type

For Darker Skin Tones (Fitzpatrick IV-VI)

• PIH affects 70% Black, 27% Asian, and 3% Latin populations in studies, with heightened severity in darker skin 8
• Exercise extreme caution with laser therapy—while it offers the only chance of complete resolution (26%), it also risks exacerbation 2, 8
• Start with lower concentrations and titrate up to minimize irritation that could worsen PIH 1, 6

Common Pitfalls to Avoid

• Do not rely on topical corticosteroids alone for PIH treatment—they may help with inflammation but are not depigmenting agents 3, 9
• Avoid aggressive procedures early—chemical peels have the highest failure rate (66.7%) and should not be first-line 2
• Do not skip photoprotection—this is the most common cause of treatment failure and repigmentation 5, 1
• Prevent irritation—excessive irritation from any treatment can paradoxically worsen PIH, particularly in darker skin 1, 6

Expected Adverse Effects

• Common side effects include desquamation, burning, stinging, dryness, and pruritus with topical agents 1
• Test for skin sensitivity before full application by applying small amounts to unbroken skin patches for 24 hours 5
• Minor redness is acceptable, but vesicle formation or excessive inflammation contraindicates further treatment 5

Monitoring and Maintenance

• Assess response at 8-12 weeks and adjust therapy accordingly 2
• Once improvement achieved, continue maintenance therapy with sunscreen and lower-potency retinoids to prevent recurrence 5
• Complete resolution is uncommon (5.4% with topicals alone, 18.1% with lasers), so set realistic expectations for partial improvement 2