The treatment of melasma and the maintenance of depigmentation represent a challenge due to its frequent recurrences. Pathophysiological mechanisms and factors have been linked to melasma such as inflammation, sun exposure, increased CD4+ T lymphocytic infiltrate and IL-17 in damaged skin. Tissue-resident memory T cells (Trm), derived from naïve T lymphocytes, are associated with the recurrence of lesions at the same sites but they have not been described in melasma. This a Cross-sectional, prospective analytical study. 20 female patients, 18 to 55 years of age, with diagnosis of melasma and mMASI score of at least 7, at least 1-year duration, lesional and perilesional skin biopsies were taken for PCR and DIF. The objective is to determine the transcription factors of Trm cells in malar melasma.

Melasma is a common, acquired pigmentary disorder characterized by chronic and relapsing hypermelanosis on sun-exposed areas that causes significant emotional and psychosocial impact in patients mainly in women with Fitzpatrick III-V phototypes. The treatment of melasma and the maintenance of depigmentation represents a challenge due to its frequent recurrences.

Different pathophysiological mechanisms and factors have been linked to melasma such as inflammation, sun exposure, increased CD4+ T lymphocytic infiltrate and IL-17 in damaged skin. In pathologies such as vitiligo and psoriasis, tissue-resident memory T cells (Trm), derived from naïve T lymphocytes, are associated with the recurrence of lesions at the same sites. These cells have a specific profile of transcription factors (Runx3+, Notch+, Blimp1+) and CD69 + CD103 + markers. These cells have not been described in melasma.

Objective: to determine the transcription factors of Trm cells in malar melasma. This is a Cross-sectional, prospective analytical study. 20 female patients, 18 to 55 years of age, with diagnosis of melasma and mMASI score of at least 7, at least1 year duration, and no treatment in the last 4 weeks, were included. Lesional and perilesional skin biopsies were taken for PCR and DIF. The presence of trm cells has not been described or studied in melasma where there is recurrence of the dermatosis in the same site, it is essential to understand its pathogenesis in order to address directed future therapies targeting these cells that may related to the disease.

Inclusion Criteria:

female patients with malar melasma, healthy volunteers 18 years of age and older, without previous treatment or photoprotection measures within the previous 4 weeks, who had at least 7 Modified Melasma Activity and Severity Index (mMASI) score

Exclusion Criteria:

• Exclusion criteria were pregnancy or nursing, menopause, coexistence of other pigmentation conditions, heat exposure, regular exer- cise, diet restriction, consumption of food supplements or any type of drugs (including anti-inflammatories and hormonal treatments) within the previous 2 months, and women who had given birth within 1 year

female patients with malar melasma, healthy volunteers 18 years of age and older, without previous treatment or photoprotection measures within the previous 4 weeks, who had at least 7 Modified Melasma Activity and Severity Index (mMASI) score