Pigmented birthmarks aren't caused by blood vessels. Instead, these markings are a result of excessive growth of the cells that make pigment (or color) in human skin. The most common types of pigmented birthmarks are café-au-lait spots, Mongolian spots and moles.
Café-au-lait spots often take on the brownish color of coffee mixed with milk, hence the name. These spots appear just about anywhere on the body. In some cases, the spots may indicate abnormal nerve tissue growth. If your child has several of these spots and the spots are larger than a quarter, be sure to see your doctor.
Pigmentation abnormalities account for Mongolian spots, too. These marks are usually bluish-gray and most often appear on the lower back or buttocks of Hispanics, Asians, Africans and other ethnicities with darker skin. Mongolian spots often completely fade by the time a child reaches school age.
Moles are extremely common pigmented birthmarks. The medical name for multiple moles is brown nevi (or brown nevus for a single mole); the word mole is Latin for spot. There are three categories of moles, including congenital, acquired and atypical moles.
About 1 percent of babies are born with congenital moles, which vary hugely in size, color, texture and overall appearance. Some have fine hair, while others have dark, thick hair. Congenital moles last for life.
Acquired moles don't appear until later in life and they're usually less than one-quarter-inch (0.6 centimeters) in size. These moles are usually, but not always, brown, and sometimes have hairs. Many medical professionals believe these moles result from skin damage caused by the sun's rays.
Atypical moles are usually a little larger than average moles. They often have irregular and poorly defined edges, and instead of an obvious brown, the color may be blotchy and run from brown into a pinkish hue. And while many common moles are simply single brown bumps on the skin, the coloration of atypical moles may affect flat portions of surrounding skin, too. These traits share similarities with melanoma, or skin cancer, so doctors carefully monitor atypical moles.