Biophysical Characteristics of Melasma Skin Comparing with the Perilesional Normal Skin and its Relation to the Melasma Subtype

Background: Melasma is a common disorder of hyperpigmentation affecting millions of people worldwide. All the exact pathways to understand the complete pathogenesis of melasma is unknown. Aims: To determine the biophysical characteristics of melasma skin compared to the normal surrounding skin. Methods: Thirty-six patients with melasma were recruited in this case-control study. The subtype of melasma (epidermal, dermal, or mixed) was determined by Wood lamp examination. The melanin index, erythema index, stratum corneum (SC), hydration, sebum content, transepidermal water loss (TEWL), temperature, friction index, and pH of lesional and perilesional normal skin of patients were measured in standardized temperature and humidity conditions. The epidermal and dermal thickness and dermal echo-density were determined on the same locations. The measurements were compared between lesional and perilesional normal skin using dependent t-test and among three subtypes of melasma using one-way ANOVA. P values of <0.05 were considered statistically significant. Results: Melanin index, erythema index, SC hydration, pH, thickness of dermis and epidermis were significantly higher and the temperature was significantly lower in lesional skin compared with surrounding normal skin. No significant differences were found in TEWL, friction index, sebum content and density of dermis. Melasma subtype, age, skintype, location and duration of melasma had no significant effect on any of these variables. Conclusions: Melasma skin is characterized by certain changes in biophysical factors of epidermis and dermis. The relation of these changes with the hyper-activity of melanocytes and melanin overproduction should be determined in future studies.