Quantifying Erythema and Skin Tone Variation in Cutaneous Rashes: A Colorimetric Approach

Accurate erythema assessment is essential in dermatologic evaluation, yet detecting erythema in diverse skin tones remains challenging. Traditional visual assessment methods, including the Fitzpatrick Skin Type Classification Scale, have limitations in darker skin tones, where erythema may be underestimated or present differently. Objective colorimetric tools, such as the SkinPhotoTyper and SkinColorCatch from Delfin Technologies Ltd, Kuopio, Finland, provide quantitative measurements of erythema and pigmentation; however, their performance across diverse skin tones remains underexplored.

A cross-sectional study was conducted among 44 patients with rashes attending an outpatient dermatology clinic. Erythema index (EI), melanin index (MI), Individual Typology Angle (ITA), and CIELAB (Commission Internationale de l'Éclairage L*a*b*) values were measured at unaffected (baseline) and affected (rash) sites using calibrated colorimetric devices. Paired t-tests compared baseline and rash measurements, Pearson correlations evaluated relationships among colorimetric parameters, and one-way ANOVA examined differences across Fitzpatrick phototypes, ITA categories, rash locations, and rash types.

As anticipated, erythema was elevated in rash sites compared to baseline, and higher melanin correlated with lower ITA and lightness. Unexpectedly, baseline erythema did not correlate with rash erythema, and darker ITA categories demonstrated higher erythema levels, suggesting that localized inflammation may not be accurately reflected by baseline skin tone or visual assessment alone.

This study supports the use of colorimetric tools across skin tones and highlights their potential in clinical assessment. Future research should focus on larger, longitudinal studies to evaluate changes in erythema and pigmentation during treatment. Such work could improve diagnostic accuracy, personalize treatment, and promote equity in dermatologic care, particularly by improving disease severity assessment, treatment decisions, and monitoring in conditions where erythema is less visually apparent.