In fact, “birthmark” is a folk term, and it is customary to call this type of skin lesions with color that babies have after birth as “birthmark”. In fact, there are many classifications of birthmarks, and in general, they can be divided into two categories: pigmented (black) and vascular (red), and the common pigmented ones include nevus of Ota, congenital pigmented nevus, coffee spot, etc.; the vascular ones include bright red nevus, strawberry hemangioma, etc. The treatment of each type of birthmark is different, but it is important to emphasize that birthmarks are not always found at birth, but may also appear gradually months or even years after birth. Mongolian spot can be one of the more common birthmarks for babies. It is formed when some melanocytes move to the epidermis and fail to cross the dermal-epidermal junction and stay in the dermis, which leads to the delayed disappearance at birth. The following characteristics are generally shown to help you identify them: (1) they are present after birth; (2) they are commonly found on the lumbosacral region, but can also occur on the buttocks or other parts of the body; (3) they are usually single round, oval or irregular light gray-blue, dark blue or brown spots. It can fade away on its own within a few years after birth without leaving any trace. The treatment of Mongolian spots is very simple and mothers and fathers do not need to worry too much, most of them do not need special treatment and can fade away on their own within a few years.