This problem exists mainly in the distribution sites of melanocytes. There are differences in the distribution of melanocytes in different parts of the body. The distribution density of melanocytes in the face and genital area is higher than that in the trunk, with about 2900±249 melanocytes per mm2 in the face and only 1100±215 per mm2 in the forearm. Moreover, the number of melanocytes decreases gradually with age, and their distribution density decreases by 8% – 10% approximately every 10 years. In addition, the distribution density of melanocytes in exposed skin was two times higher than that in non-exposed areas.