Melanocytic activation is a type of longitudinal melanonychia (LM) that results from increased pigmentation in the nail matrix epithelium and nail plate without a corresponding increase in melanocyte count [1, 2]. Melanocytic activation typically presents as a gray longitudinal band, involving a single nail or multiple nails. In adults, melanocytic activation is by far the most common cause of melanonychia [2]. Physiologically, trauma, infection, or inflammation can activate nail matrix melanocytes, leading to increased pigment production [3, 4]. Melanocyte activation initiates melanin synthesis, and melanin-rich melanosomes are then transferred to differentiating matrix cells via dendrites. These cells migrate distally and eventually transform into nail plate onychocytes, resulting in visible pigmentation within the nail plate [4].