Gaps in Post-Inflammatory Hyperpigmentation Research for Skin of Color

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Post-inflammatory hyperpigmentation (PIH), the darkening of the skin due to the activation of melanocytes by inflammatory mediators, tends to be more prominent and enduring in individuals with darker skin tones. A recent review recognized skin of color (SOC) individuals (Fitzpatrick skin type (FST) III-VI) as having an increased size of melanosomes, quantity of melanin, and increased eumelanin.¹

According to the review, PIH can result in “significant psychosocial distress and a diminished quality of life” for affected individuals. Researchers stated that despite the impact, research on PIH treatment has traditionally been centered around lighter skin tones, leading to noticeable disparities in care. While treatment options are already limited, there is also a lack of efficacy data applicable in SOC.² 

The review identified common therapeutic approaches as topical treatments such as retinoids, tranexamic acid (TXA), and hydroquinone. Researchers also stated the further investigation into light and laser therapy is being conducted.³

Methods and Demographics

The review included data on any person with SOC diagnosed and undergoing intervention for PIH, regardless of age, sex, disease severity, treatment type, or comorbid conditions. Eligible studies included randomized controlled trials (RCTs), cohort (prospective and retrospective) studies, cross-sectional studies, case-control studies, case-series, and case reports.

Overall, 46 studies were included in the review, summarizing the experiences of 1356 SOC patients. Most of the studies came from the US (31%), Korea (11%, China (9%) and the United Kingdom (9%), with study types including 31% case reports, 30% experimental studies, and 27% randomized controlled trials (RCTs).

The mean age of included individuals was reported as 29 years (n = 1036), with 78% being female. Researchers reported the ethnicity/race distribution in 849 participants as: Black (70%), Asian (27%), Hispanic/Latin (3%), and other (0.2%). They received no reported cases among Middle Eastern/Arab, Pacific Islander, or Indigenous categories. Of 570 cases with available data on FST, the review stated that FST III accounted for 20%, FST IV for 40%, FST V for 34%, and FST VI for 6%.

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In 1225 of the 1356 cases, precipitating factors contributing to the development of PIH were reported. The review recognized acne as the predominant cause (97%; n = 1060), with inflammatory conditions accounting for 89% of total cases (n = 1089). Trauma related PIH constituted 11% of the cases (n = 134), with researchers reporting the following statistics:

Results

The review stated that among the 346 (26%) participants who did not receive treatment, none saw complete resolution (CR), 62% achieved partial pigment reduction, 4% achieved partial size reduction, and 33% had no response (NR). The average time to resolution was 68 days, with a follow-up period of 3 months.

The review found topical treatments to be common, with 294 participants using topical retinoids, though none saw complete resolution. Of these, researchers stated that 64% had partial pigment reduction, 21% had partial size reduction, and 14% experienced no response. The average follow-up time for topical retinoids was reported as 4 months. Laser therapy, applied to 227 participants, resulted in 26% complete resolution, 66% partial pigment reduction, and 33% no response, with an average resolution time of 140 days and follow-up of 8 months. The review stated chemical peels used by 123 participants led to partial pigment reduction in 67% of cases and no response in 33%, with an average resolution time of 28 days and a follow-up period of 4 months.

Among topical monotherapies, researchers found retinoids such as tretinoin, adapalene, and tazarotene showed partial improvement but did not achieve complete resolution. Topical steroids were found to provide partial improvement, with 0.05% desonide showing a significant reduction in lightness index values. The review stated bakuchiol was effective in treating trichloroacetic acid-induced PIH but not acne-induced PIH, while cysteamine cream resulted in a notable reduction in melanin index in 1 case.

Researchers stated combination therapies yielded promising results, particularly when compounded hydroquinone formulations and chemical peels were used together. Chemical peels combined with other treatments showed more significant improvements compared to laser therapy alone. However, the review found no single combinatorial regimen was distinctly superior, though some partial improvements were observed.

Device-based treatments included various laser therapies, such as the 1064 nm QS Nd, 755 nm alexandrite picosecond, and 1927 nm thulium fiber lasers, all of which researchers found to show significant PIH reduction. The QS ruby laser was reported to be less effective and potentially worsened PIH. The review stated that Intense Pulsed Light therapy demonstrated moderate efficacy with minor side effects, while High-Intensity Focused Ultrasound showed variable results and some adverse effects.

Chemical peels, including salicylic acid, glycolic acid, and lactic acid peels, were reported to be partially effective, with side effects like redness and dryness. Oral isotretinoin resulted in near-complete resolution in one study without any adverse events. Overall, the review stated that while no single treatment universally resolved PIH, a combination of therapies, especially lasers and chemical peels, showed the most promise with varying degrees of effectiveness and tolerability.

Conclusion

Despite a disproportionate effect of PIH on SOC individuals, the review recognized a paucity of research on treatment efficacy. Through this review, researchers highlighted a “critical need” for the development of a universal PIH scale. They found laser therapy to emerge as one of the few modalities capable of completely clearing PIH in select SOC individuals, but with associated high costs and risks of adverse effects. Researchers stated that numerous safe treatment options, such as topical retinoids, exist for SOC individuals and warrant further exploration. The review found that while there is substantial room for improvement, there is also “considerable” optimism for enhancing intervention strategies in the future.

References

1. Mar K, Khalid B, Maazi M, et al. Treatment of post-inflammatory hyperpigmentation in skin ofcolour: A systematic review. J Cutan Med Surg. July 29, 2024. doi:10.1177/12034754241265716
2. Maghfour J, Olayinka J, Hamzavi IH, et al. A focused review on the pathophysiology of post-inflammatory hyperpigmentation. Pigment Cell Melanoma Res. 2022;35(3):320-327. doi:10.1111/pcmr.13038
3. Kashetsky N, Feschuk A, Pratt ME. Post-inflammatory hyperpigmentation: A systematic review of treatment outcomes. J EurAcad Dermatol Venereol. 2024;38(3):470-479. doi:10.1111/jdv.19566