A birthmark is a congenital, benign irregularity on the skin which is present at birth or appears shortly after birth—usually in the first month. They can occur anywhere on the skin. Birthmarks are caused by overgrowth of blood vessels, melanocytes, smooth muscle, fat, fibroblasts, or keratinocytes. Dermatologists divide birthmarks into two types: pigmented birthmarks and vascular birthmarks. Pigmented birthmarks caused by excess skin pigment cells include: moles, café au lait spots, and Mongolian spots. Vascular birthmarks, also called red birthmarks, are caused by increased blood vessels and include macular stains (salmon patches), hemangiomas, and port-wine stains. A little over 1 in 10 babies have a vascular birthmark present by age 1. Several birthmark types are part of the group of skin lesions known as nevi or naevi, which is Latin for "birthmarks". Birthmarks occur as a result of a localized imbalance in factors controlling the development and migration of skin cells. In addition, it is known that vascular birthmarks are not hereditary. Pigmented types Mole Congenital melanocytic nevus is a type of melanocytic nevus, the medical term for what is colloquially called a "mole", found in infants at birth. Occurring in about 1% of infants in the United States, it is located in the area of the head and neck 15% of the time, but may occur anywhere on the body. It may appear as light brown in fair-skinned people, to almost black in people with darker skin. Coming in a variety of sizes and appearances, they may be irregular in shape and flat, or raised and lumpy in appearance and feel. Such naevi can also manifest themselves as beauty marks, which most commonly appear on the face, neck or arms. Café au lait spot Café au lait spot macules may occur anywhere on the body. They are most commonly oval in shape and light brown, or milk coffee, in color. These birthmarks may be present at birth, or appear in early childhood, and do not fade much with age. One or two on an individual is common; however, four or more may be an indicator of neurofibromatosis. In the event of weight gain, the birthmark can stretch with the skin and become larger. Mongolian spot A Mongolian blue spot (dermal melanocytosis) is a benign flat congenital birthmark with wavy borders and irregular shape, most common among East Asians and Turkic people (excluding Turks of Asia Minor), and named after