The term “Mongolian blue spots” is now considered inappropriate and outdated. The condition is currently referred to as slate gray nevi, or lumbosacral dermal melanocytosis. It is a type of birthmark.

Also known as blue-gray spots and congenital dermal melanocytosis, the marks are often present at birth but may also appear during the first weeks of life. They usually disappear by the age of about 3–5 years, but they can remain into adulthood.

It is not possible to prevent slate gray nevi from forming, and experts do not know why some infants have them while others do not.

The marks occur when some of the skin’s pigment cells, or melanocytes, get “trapped” in the deeper layers of skin during the infant’s development. When the pigment does not reach the surface, it appears as a gray, greenish, blue, or black mark.

Mongolian blue spots on a mans backShare on Pinterest
Slate gray nevi often disappear at about 3–5 years of age.
Image credit: Gzzz, 2016.

No one knows precisely what causes slate gray nevi, but some infants are more likely than others to get them. They are more likely to affect people with darker skin, including those with Asian, Hispanic, Native American, African, or East Indian ancestry.

The spots usually occur on the lower back, buttocks, and upper legs.

The marks are flat and smooth and may look like bruises. But, unlike bruises, they do not cause pain and do not result from an injury.

According to a 2013 review, slate gray nevi affect about 10% of white babies, 50% of Hispanic babies, and 90–100% of Black and Asian babies.

Some argue, however, that on microscopic inspection, all babies are born with some kind of birth mark due to pigmentation.

The American Academy of Dermatology note that the spots are most common in babies of Asian ancestry.

Slate gray nevi are harmless, but they can occasionally occur alongside some rare diseases that affect a person’s metabolism, such as:

  • Hurler’s disease
  • Hunter’s syndrome
  • Niemann-Pick disease
  • mucolipidosis
  • mannosidosis

The link may be more likely in those with marks that are large and widespread or on areas outside the back and buttock regions.

Slay gray nevi may also occur with other birthmarks linked to vascular features or pigmentation, such as café-au-lait macules.

Doctors have noticed slate gray nevi occurring with the following conditions, too, although it is unclear whether there is a link:

  • Sjogren-Larsson syndrome
  • leptomeningeal melanocytoma involving the spinal cord
  • occult spinal dysraphism

Learn more about different types of birthmarks.

Soon after delivery, a doctor will examine any marks that the newborn may have and document them in the baby’s medical record.

Parents, caregivers, and healthcare professionals can check the spots at regular intervals to determine whether they are going away on their own as the child grows. Most slate gray nevi disappear in time.

Is treatment necessary?

People with slate gray nevi do not need any special care unless the marks occur alongside another condition. They are not painful and do not pose a health problem.

According to the American Society for Dermatologic Surgery, they require no treatment.

Laser removal

If slate gray nevi persist into adulthood, and a person finds them bothersome, removal procedures may be an option.

In a small study in Japan, professionals used a device called an alexandrite laser to treat slate gray nevi in 16 people. Overall, they concluded that the treatment was successful. However, two participants left the study as they were not happy with the results, and two experienced hyperpigmentation after the treatment.

The results of another study in Japan suggest that treatment might be more successful before the age of 20 years. The authors also concluded that adjusting the timing of sessions to optimize the intervals might lower the risk of skin darkening as a side effect.

As slate gray nevi can resemble bruises, there have been cases where doctors and health visitors have suspected child abuse in children who have them.

Documenting any birthmark from an early age can help prevent such confusion. A doctor can also distinguish bruises from slate gray nevi by checking whether the mark:

  • is tender
  • changes over time
  • disappears within days or weeks

Slate gray nevi are painless and do not change. If they do disappear, this will take several months.

Slate gray nevi are a type of birthmark. They are not usually a cause for concern. However, in rare cases, they can be a sign of a disorder that needs medical attention.

If a medical professional assesses the infant and finds slate gray nevi but no signs of any other health issue, parents and caregivers do not need to worry.

The marks usually disappear during early childhood. If they remain, and a person finds them bothersome, a doctor or dermatologist may be able to offer advice on treatment options.