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.

[1] They are caused by overgrowth of blood vessels, melanocytes, smooth muscle, fat, fibroblasts, or keratinocytes.

Birthmarks occur as a result of a localized imbalance in factors controlling the development and migration of skin cells.

[6] Usually, as multiple spots or one large patch, it covers one or more of the lumbosacral area (lower back), the buttocks, sides, and shoulders.

[6] It results from the entrapment of melanocytes in the dermis during their migration from the neural crest to the epidermis during embryonic development.

[7] Colloquially called a "stork bite", "angel's kiss" or "salmon patch", telangiectatic nevus appears as a pink or tanned, flat, irregularly shaped mark on the knee, back of the neck, and/or the forehead, eyelids and, sometimes, the top lip.

[8] PHACES Syndrome, a rare condition that often involves brain, heart, and arterial abnormalities, is generally accompanied by the presence of large facial hemangiomas.

Port-wine stains, also known as nevus flammeus and sometimes mistaken for strawberry marks, are present at birth and range from a pale pink in color, to a deep wine-red.

Irregular in appearance, they are usually quite large, and caused by a deficiency or absence in the nerve supply to blood vessels.

[9] Over time, port-wine stains may become thick or develop small ridges or bumps, and do not fade with age.

In another case, a large red mark on a baby's cheek was caused by the mother seeing a man shot down at her side, when the discharge of the gun threw some of the blood and brains into her face.