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Congenital nevus

What is a congenital nevus?

A congenital nevus (con-JEHN-ah-tull NEV-us) is a type of mole that some babies are born with. Something that is congenital is present at birth. Nevus is the medical term for a mole. A congenital nevus is a very common type of birthmark.

Another name for this type of mole is congenital melanocytic nevus (CMN). Melanocytes are cells that make pigment, or color. These types of moles form when the melanocytic cells clump together instead of spreading evenly in the skin. Some of these moles may show up later when a baby is 2 or 3 years old. These late-forming types are called tardive congenital nevi.

More than one nevus are called nevi.

What do they look like?

Smaller CMNs are usually round or oval shaped. They are frequently raised but can also be flat. They are usually smooth and the same color across the whole mole. Smaller CMNs are usually brown or black, with some being tan or pink. Some may have hair.

Larger CMNs may have an irregular shape and multiple colors. They may also feel rough to the touch and have extra hair. The largest CMNs sometimes have smaller moles surrounding them, called satellite nevi.

CMNs can be anywhere on the body, with the most common locations being the lower back and thigh. They are also commonly found on the head/face, neck, feet and hands.

A congenital nevus stays on the skin for life and grows as the baby grows, covering about the same amount of skin on the adult as it did on the baby proportionally. In some cases, they lighten in color over time.

They range in size

CMNs can be very tiny or big enough to cover a large area of the body. There are different types of CMN based on how big they are likely to be in adulthood. Moles on the head tend to double in size; ones on the body, arms and legs tend to triple in size. As the child ages, they may also change in color and texture.

The categories of congenital nevi, based on the adult size, are:

• Small: less than 1.5 cm, or about 5/8 inch.
  Small CMNs are common, occurring in about 1 in every 100 newborns.
• Medium: Between 1.5 and 20 cm, or about 5/8 to 8 inches
  These are not as common as small CMNs, but still not rare. They affect about 1 in 1000 babies.
• Large: 20 to 40 cm, or about 8 inches to just under 16 inches
  These large moles are rare.
• Giant: Greater than 40 cm or around 16 inches
  A giant congenital nevus is extremely rare, affecting between 1 and 20,000 to 1 in 500,000 newborns.

Another specific type of congenital nevus is called a speckled lentiginous nevus. These moles have a tan or light brown color with darker colored spots, similar to freckles, on top. They also can range in size.

Causes and symptoms

Researchers don’t know what causes congenital nevi. They don't appear to be inherited. Researchers do know that the earlier these CMNs begin developing in the womb, the larger they are at birth.

Fortunately, CMNs usually don’t hurt. Sometimes they may be a little bit itchy. If that’s the case, using a good, fragrance-free moisturizer may help.

When to be concerned

Because babies are born with these moles, you should see your baby’s doctor if you notice a large, colored place anywhere on the skin. However, just remember that almost all congenital nevi are harmless. This is especially true for small and medium CMNs.

Large and giant CMNs do need to be watched because sometimes these can turn into a type of skin cancer called melanoma. However, even though large and giant CMNs do have this risk, it is still low overall.

If your child has a congenital nevus of any size, you should see a doctor if it:

• changes in color or shape
• starts bleeding, scabbing or hurting

What is the cancer risk?

The good news is that small and medium congenital nevi have less than 1% chance of changing into cancer. For these babies, usually nothing needs to be done other than parents and pediatricians watching them for changes.

If your baby has a large or giant CMN, or many different CMNs, your baby’s doctor may refer you to a pediatric dermatologist for another look and possible testing. For removal, particularly in larger CMNs, you will likely be referred to a plastic surgeon.

In a small percentage of babies with giant CMNs, melanocyte cells collect in the baby’s brain and spinal cord. This condition is called neurocutaneous melanocytosis. When this happens, sometimes it can cause symptoms such as:

• headaches
• vomiting
• irritability
• seizures
• developmental issues

If there is a concern for neurocutaneous melanocytosis your doctor will order a magnetic resonance imaging (MRI) study.

Treatment: Watch or Remove

The decision to watch or remove a congenital nevus depends on several factors, and it’s important to take all of them into consideration.

The most important point is the risk for cancer. Small and medium congenital nevi are extremely unlikely to develop into cancer. Large and giant nevi have a higher risk but sometimes removing them can leave big scars that are as noticeable as the CMN. And, especially for giant CMNs, skin cancer may develop in other places, so removing the CMN may not completely eliminate the cancer risk.

Another factor is the CMN’s location. For example, a small nevus on the scalp has a very low risk of cancer, but it might be removed because, covered with hair, it would be hard to check.

Shape and consistency are other factors. On a mole that has an irregular shape or is lumpy or thick, it may be harder to see changes if they happen. These might be removed just to be on the safe side.

The psychological effect on the child is another thing to think about. If a mole is in a conspicuous place or if it is hairy and dark, it may make the child feel bad about how it looks.

Talking with your baby’s doctor about all these points can help you understand your options.

Congenital nevus removal

If a small or medium mole needs to be removed, sometimes doctors will wait until a child is old enough to handle a shot with numbing medication, at around age 10 to 12. For small moles, the surgeon may perform a simple one-step excision with direct wound closure. In this procedure, the surgeon cuts the mole out of the skin and sews the skin back together all in a single operation.

For large and giant CMNs, removal is more complicated. It may require several incisions with stitches and possibly skin grafts. These are likely to cause scars, although our Children’s of Mississippi plastic surgeons are experts in reducing scarring as much as possible. Some giant CMNs may be too large to completely remove.

Our pediatric plastic surgeons at Children’s of Mississippi will carefully evaluate your child to make sure they can offer the best chance to heal without a major scar or loss of any function.

Get help for a congenital nevus

The plastic surgeons at Children’s of Mississippi are specialists in evaluating and removing CMNs. They can help you understand what treatment options are available for your child’s specific situation. Schedule an appointment online.

Last reviewed: Sept. 15, 2025