What to Know About Mongolian Blue Spots

Medically Reviewed by Poonam Sachdev on December 16, 2021
3 min read

Congenital dermal melanocytosis — more commonly known as Mongolian blue spots — is a kind of birthmark commonly found in newborns. Also known by the name slate gray nevus, Mongolian blue spots often appear right at birth or in the first few weeks of life.

They are harmless and do not need to be removed.

These marks may look like bruises, but they're not. The size, shape, and color of a bruise can change in a matter of days, while congenital dermal melanocytosis often stays on the skin for some years. Mongolian birthmarks are also not painful to touch. They are flat and have the same texture as normal skin.

A baby can also have one spot or several of them. The shapes range from oval, round, and irregular. In most cases, the birthmarks don't cover more than 5% of the body.

The birthmarks can range in size from a few millimeters to more than 10 centimeters. 

These pigmented birthmarks show up in certain regions of the body, including:

  • The buttocks
  • The back
  • The shoulders
  • The base of the spine

Because these marks are on the buttocks more than any other part of the body, Mongolian blue spots are sometimes called “blue butt”.

The name Mongolian blue spots came about because the spots were most commonly found in children of Mongolian or other Asian ancestries.

Mongolian blue spots happen when pigment cells make melanin under the skin’s surface. The reason the spots are blue is because of something called the Tyndall effect. The Tyndall effect involves the scattering of light as it passes through particles in its path.

The pigments on the surface of the skin appear in different combinations of blue, gray, and black because they have a shorter wavelength. The number of melanocytes often helps determine the mark's specific color or combination of colors. 

Melanocytes are cells that produce melanin, which causes pigmentation in the skin. Other factors that decide the color of the spots include how much melanin is there in these cells as well as how deep the spots are in the dermis.

Mongolian blue spots are still most common among Asian children and in those with darker skin. Some of these groups include the children of Polynesian, Indian, and African descent.

On average, only about 10% of Caucasian infants have Mongolian blue spots. Blue spots are found in about 50% of Latinos, and 90% to 100% of Asian and African populations.

Mongolian blue spots are not cancerous, nor linked to any diseases. However, if you notice your child's blue spot or spots becoming larger or more revealing — especially near the mouth -- consult a pediatrician.

A few studies have also found a link between Mongolian blue spots and certain metabolic problems, like those that fall under lysosomal storage diseases. Studies show this association more so in cases of extensive blue spots.

For most babies, the blue spots go away on their own, usually between ages 3 and 5. However, some people have the birthmarks into adulthood.

Adults who still have Mongolian birthmarks on their bodies may be able to remove them through laser treatment.

Patients considering laser treatment for Mongolian blue spots for cosmetic reasons may also want to consider using makeup or covering the birthmarks with clothing if they are bothersome.

In most cases, Mongolian blue spots shouldn't cause parents any concern because there are no medical complications associated with it. More often than not, these spots are just like any other birthmarks. They're also very likely to disappear with time, rarely persisting past age 6.

Parents of children with Mongolian blue spots should talk to their child's pediatrician if they have any concerns.