The etiology of this disease is not clear, and it may be genetically related to autosomal dominant inheritance. During embryonic development, when melanocytes migrate from the neural crest to the epidermis, for some reason they fail to pass the epidermal and dermal junction and remain in the dermis and form lesions. Some studies suggest that it may not be a residue of melanocytes, but a kind of misshapen tumor or nevus-like damage similar to blue nevus. Most of the nevus of Ota lesions are distributed in the area of the first and second branches of the trigeminal nerve. The distribution of this disease along the peripheral nerve suggests that melanocytes may come from the peripheral nerve tissue. The occurrence of nevus of Ota may be due to some melanocytes failing to cross the junction between the dermis and the epidermis when moving to the epidermis, and staying in the dermis or below the dermis for a long time. Melanocytes in the middle of the dermis contain varying amounts of melanin granules scattered between the collagen fibers of the dermis. In slightly elevated and infiltrated pigmented spots, the number of melanocytes is more, similar to that of blue nevus, especially in the nodular damage area, which is indistinguishable from blue nevus. The infiltration of melanocytes can also be found in deeper structures in the eye, including the orbital periosteum. But the nature of nevus of Ota is the same regardless of the time of formation and is not different. For those patients with nevus of Ota formation at birth or shortly after birth, it usually fluctuates once when they are around 4-5 years old and once when they are 12-14 years old, which means that during this period, the nevus of Ota formation will grow a little larger or darker, and is more stable later. The color of nevus of Ota can change with the seasons, such as darker in summer and lighter in winter, and emotions also have an effect on the color. The treatment of nevus of Ota is for cosmetic purposes, and its principle should be to remove the pigment of skin lesion without leaving scar and without causing pigmentation or loss. In the past, various treatments, such as dry ice compression method, liquid nitrogen freezing, skin grinding, skin implantation, skin peeling method, C02 laser treatment and even radionuclide treatment, can reduce the pigment of skin lesions, but it is difficult to get a complete cure, and it is easy to cause scar or pigment loss, and the treatment process is painful and the efficacy is extremely unsatisfactory. Laser treatment for nevus of Ota is the most effective method at present. Depending on the color of nevus of Ota, it usually takes about 2-4 times of treatment, with an interval of two months. The treatment time takes about 20-30 minutes each time. At present, the commonly used lasers are 755nm emerald laser, 1064nm Nd:YAG laser, 694nm ruby laser, etc. These lasers all adopt Q modulation technology.