Mongolian spots are flat, blue-gray or slate-colored birthmarks, most often on a baby's lower back and buttocks. Many doctors now call them congenital dermal melanocytosis or slate gray patches. They are harmless, they are very common in Black babies, and most fade by early childhood. The one real risk is not to the baby's health: a large or unusual patch can be mistaken for a bruise, so it should be written down in your baby's records early.
What these birthmarks look like on a Black baby
The patches are flat, with the same texture as the skin around them. MedlinePlus describes them as blue or blue-gray, with irregular shapes and unclear edges, usually at least 2 centimeters wide (MedlinePlus, reviewed 2025). A 2013 review describes a color range from blue to greenish, gray or black, and sizes from a few centimeters to more than 20 (Gupta and Thappa, 2013).
On brown and Black skin the color is often closer to slate or charcoal than to bright blue, which is part of why the newer name "slate gray patch" fits. A forensic study published in 2020 notes that the color depends on skin type and can shade into purple, dark blue-red and brown-black tones (Kettner et al., 2020).
The usual location is the lower back, the top of the buttock crease and the buttocks. Patches also show up on the upper back, shoulders, arms and legs. A baby may have one small patch or several large ones.
How common they are, and why the numbers differ
Every study agrees these birthmarks are far more common in babies with darker skin. The exact share depends on who did the counting and how. The classic 1981 study by Cordova counted them in 96.5% of 259 African American newborns, 46.6% of Hispanic newborns and 9.3% of white newborns. A larger prospective US study in 2012, using updated classifications, counted them in 32.1% of 193 African American newborns, 25.7% of Hispanic newborns and 6.7% of white newborns. Both figures are tabulated side by side in the 2020 review (Kettner et al.; Kanada et al., 2012).
The practical takeaway is the same either way: in Black families these birthmarks are an ordinary finding, not a rare one, and every clinician who examines Black infants should expect to see them.
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See a doctor todayWhy they happen
Melanocytes, the cells that make pigment, travel to the skin while a baby develops in the womb. In these birthmarks some of them stay in the deeper layer of the skin, the dermis, instead of finishing the trip to the surface. MedlinePlus explains that the color comes from that collection of melanocytes in the deeper layers (MedlinePlus). Pigment that sits deep in the skin reads blue-gray rather than brown.
Nothing the parent did causes them. They are not a sign of a hard delivery, a fall, or anything that happened during pregnancy.
When they fade
The 2013 review says the color is most intense around age 1 and then gradually fades, and the patches are rarely seen after age 6 (Gupta and Thappa). MedlinePlus says they often fade in a few years and are almost always gone by the teen years (MedlinePlus). Patches outside the lower back, on the shoulders, arms or face for example, are more likely to persist (Alimi et al., 2018).
No treatment is needed for typical patches. For a persistent patch in a visible spot that bothers an older child or adult, a dermatologist can talk through laser options, but that is a cosmetic choice, not a medical one.
The bruise problem, and how to protect your family
Because they can look like bruises, these birthmarks have been mistaken for signs of abuse. The 2013 review says patches on the back of the head, temple, jaw, shoulders and limbs can be confused with bruises from child abuse, "thus necessitating documentation at birth" (Gupta and Thappa). MedlinePlus is plain about it: dermal melanocytosis is a birthmark, not bruises (MedlinePlus).
There is a simple way to tell them apart over time. A bruise changes within days: it swells or feels tender, then shifts through purple, green and yellow as it heals. A birthmark stays the same color and shape week after week and does not hurt when touched. In the forensic study, examiners scheduled a second look two to six weeks later whenever they were unsure, because a true bruise would have changed by then and a birthmark would not (Kettner et al.).
What to do as a parent:
- At the newborn exam or first pediatric visit, ask the clinician to record every patch in the chart, with location and approximate size.
- Take your own dated photos in good daylight, with a coin or ruler next to the patch for scale.
- Tell anyone who cares for your baby, including daycare staff and relatives who change diapers, that your child has these birthmarks and where they are.
- If your child sees a new doctor, emergency department or urgent care clinic, mention the birthmarks before the exam.
When to see a doctor
A typical patch on the lower back needs nothing more than documentation. Talk to your child's pediatrician if:
- The patches are very large or widespread, cover much of the back and limbs, or keep increasing after the first months. Extensive or persistent patches have been linked in case reports to rare inherited conditions, including lysosomal storage diseases, so a pediatrician may look for other signs (Alimi et al.).
- Your baby also has weak muscle tone, feeding trouble or other health or development concerns. A birthmark alone does not suggest illness, but extensive patches together with symptoms like these have been reported in rare metabolic conditions such as GM1 gangliosidosis, so they should be looked at together (Ranjan et al., 2018).
- A patch is raised, lumpy, tender or changing color. That is not how these birthmarks behave.
- A blue-gray patch is around the eye or on the white of the eye. That can be a related but different birthmark, nevus of Ota, which sits in the area of the eye and cheek and tends to persist rather than fade (Kettner et al.).
Get care the same day for any mark that looks like a bruise and comes with swelling, pain, a limp, crying when touched, or a story that does not fit. If you are ever worried about a child's safety, call your pediatrician or the Childhelp National Child Abuse Hotline at 1-800-422-4453. If a child is in immediate danger, call 911.
Frequently asked questions
Are Mongolian spots normal in Black babies? ▼
Yes. They are one of the most common birthmarks in Black newborns. Studies of US newborns have found them in roughly a third to nearly all Black babies, depending on the study.
Why are they called Mongolian spots? ▼
It is an old name that is still common on medical records. MedlinePlus and many clinicians now use dermal melanocytosis or congenital dermal melanocytosis, which describes what the mark is rather than tying it to one population.
Do Mongolian spots go away? ▼
Most fade during early childhood and are rarely seen after about age 6. Patches outside the lower back are more likely to last longer, and a few persist into adulthood.
How can I tell a Mongolian spot from a bruise? ▼
A birthmark is flat, painless, and the same color and shape for weeks. A bruise is often tender or swollen and changes color over days as it heals. When in doubt, a recheck in two to six weeks settles it, and documentation from birth prevents the question in the first place.
Do they need treatment? ▼
No. Typical patches are harmless and fade on their own. Treatment is only considered, by choice, for a persistent patch in a visible spot later in life.
