The lack of an objective method to histopathologically classify melasma as epidermal, mixed, or dermal led the authors to develop an empirical formula that would allow the melanin existing in the dermis in melasma cases to be quantified. Thus, from histology slides of a historic series of melasmas in women, a cross-sectional study was designed with the goal of classifying melasma cases according to the quantity of dermal melanin deposits. Through this study, a quantitative classification method was proposed. Data from 50 women with clinically and histopathologically confirmed melasma were analyzed for the following variables: age, skin color, melasma progression time, age at menarche, irregularity of menstrual cycles, total pregnancies, full-term pregnancies, oral contraceptive use, attributable cause, and topographic classification according to the histopathologic classification and the quantity of melanin in the dermis as expressed by the dermal melanin concentration index (DMCI). According to the histopathologic classification, 58% of melasma cases were epidermal, 24% were mixed, and 18% were dermal; according to the topographic classification, 82% were central. The distribution of cases by the DMCI was one tailed, with a discrete bimodal tendency. When comparing melasma types classified by histopathology, the only differences noted were with the use of oral contraceptives, which was more frequent among women with dermal melasmas. A moderate correlation between age and the DMCI and between the number of pregnancies and the DMCI was identified. There was a strong positive correlation between DMCI and histopathologic classification (rSpearman=0.571; P<.001). We concluded that, in melasmas in women, it is possible to determine an index that would translate the quantity and size of melanin deposits in the dermis and classify them as epidermal, mixed, or dermal. In this study, this index was the DMCI. Because this distribution is quantitative, it shows favorable performance in distributing and correlating melasma types.