-What is congenital nevus? First of all, we should start from the definition of melanocytic nevus. Melanocytic nevus is a kind of pathological melanocyte aggregation, which is divided into congenital and acquired, as the name suggests, congenital means born with it. Congenital melanocytic nevi are very common, with one in a hundred newborns suffering from congenital nevi. However, congenital macromegaly is uncommon, with an incidence of only 1 in 20,000. Among them, the simplest definition is that a nevus larger than 20 cm in diameter is called a giant nevus in adults, and for a newborn baby, this corresponds to a value of 9 cm. The most common site for giant nevus is the trunk, followed by the extremities, and the least common is the head and neck. Giant nevus in newborn babies is usually hairless, light brown, flat and does not protrude from the skin surface. As the child grows, the hair on the surface of the giant nevus increases, and the color gradually increases or becomes uneven, and the texture becomes rough, sometimes warty, sometimes nodular. 80% of giant nevi are accompanied by one or more small nevi scattered all over the body, called satellite nevi. Giant nevi grow in proportion to the body, and the color, texture, and hairiness of the nevus may change. Giant nevi usually develop black, coarse hair and darken in color by the time the child is 1-2 years old. Around the age of 10, the giant nevus becomes elevated, warty and hyperkeratotic, and the hairs become rougher, but the color of the nevus tends to fade. The above traits of giant nevus will gradually become stable in adulthood.