Hyperpigmentation may signal ongoing inflammation

Dermatologists use the term postinflammatory hyperpigmentation (PIH) to describe darkened skin that remains after an inflammatory disorder has subsided. But the inflammation may not always be over, and a JAMA Dermatology viewpoint argues that the term “postinflammatory” may obscure persistent disease activity, particularly in patients with darker skin tones.

Dr. Jerry Tan

The authors point out that hyperpigmentation can coexist with ongoing inflammation, particularly in chronic or recurrent conditions such as acne, atopic dermatitis, and lichenoid disorders. Describing the pigmentation as “postinflammatory,” they write, may lead clinicians to regard it as a biologically inactive sequela and focus treatment on pigment reduction alone.

That assumption may be especially consequential in patients with darker skin tones, in whom epidermal melanin can reduce the visible appearance of erythema. As a result, inflammation may persist even when redness is subtle or clinically inapparent. The author group included dermatologists Dr. Jerry K.L. Tan (Windsor, Ont.), Dr. Iltefat H. Hamzavi (Detroit), Dr. Tasneem F. Mohammad (Detroit), and Dr. Andrew F. Alexis (New York City).

They cited a prospective study of 29 participants with Fitzpatrick skin types II through VI published in the British Journal of Dermatology. Over 35 days, acne lesions clinically classified as PIH continued to show both hyperpigmentation and erythema on objective colorimetric assessment, although clinician-rated erythema declined. Histologic research using a related experimental model also identified persistent perifollicular and perivascular lymphocytic infiltration 28 days after inflammation was induced.

Evidence from other dermatoses points in the same direction. Hyperpigmentation improved with interleukin-13 blockade in a phase 3b study of lebrikizumab for moderate-to-severe atopic dermatitis in patients with darker skin tones. Improvement reported with topical Janus kinase inhibition in lichen planus pigmentosus likewise suggests that immune signalling may contribute to some pigmentary changes.

The authors do not propose abandoning PIH altogether. Instead, they recommend reserving the term for cases in which inflammatory activity has reasonably resolved. When inflammation remains possible, descriptors such as acne-associated hyperpigmentation or the broader “inflammation-associated hyperpigmentation” may more accurately reflect the underlying biology.

No specialized imaging or routine biopsy is required, they add. Clinicians can assess itch, tenderness, subtle induration or scale, as well as recurrence or evolution within the same distribution.

According to the authors, the proposed change is partly linguistic but has clinical implications: more precise terminology may discourage premature diagnostic closure and prompt clinicians to treat persistent inflammatory disease in tandem with the pigmentation it produces.