AbstractBackgroundThe difference in skin pigmentation induced by blue light between melasma patients and healthy people has not been reported. This study aimed to explore the impact of different doses of blue light irradiation on the pigmentation of the skin of non‐exposed areas in female melasma patients with III‐IV‐type skin and healthy women.Materials and methodsThis observational study enrolled patients with melasma and healthy people at the First Affiliated Hospital of Kunming Medical University between January and April 2021. The outcomes were the degree of pigmentation, ΔL*, and ΔITA* values.ResultsForty‐two (21/group) participants were enrolled. After irradiation with different doses of blue light, different degrees of pigmentation could be observed in the irradiated area of the skin of female melasma patients and healthy women. The △L* and △ITA* values in the irradiated area of the skin of healthy women were higher than in female melasma patients after blue light irradiation at 20 J/cm2(p< 0.05). There were no significant differences in the pigmentation scores, △L* values, and △ITA* values in the irradiated areas of skin at different time points after irradiation with the other doses of blue light (p> 0.05).ConclusionBlue light at 20 J/cm2induced a smaller change in pigmentation in melasma patients than in healthy women, but the effect of blue light at 40–80 J/cm2was similar.