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Congenital Melanocytic Nevus

Last updated June 16, 2022

Reviewed by: Lester Fahrner, MD

Approved by: Krish Tangella MD, MBA, FCAP

Congenital Melanocytic Nevus (CMN) is a common melanocytic mole that is present at birth, or develop immediately following birth, on the skin of the baby. It may be present anywhere on the body.

What are the other Names for this Condition? (Also known as/Synonyms)

  • CMN (Congenital Melanocytic Nevus)
  • Congenital Melanocytic Naevus

What is Congenital Melanocytic Nevus? (Definition/Background Information)

  • A nevus (plural nevi) is a mole on the skin that can occur on any part of the body. A melanocytic nevus is benign tumor of melanocytic (pigment-based) cells that occur on the skin
  • Congenital Melanocytic Nevus (CMN) is a common melanocytic mole that is present at birth, or develop immediately following birth, on the skin of the baby. It may be present anywhere on the body
  • Congenital Melanocytic Nevus may occur as a round or oval shaped macule, papule, or plaque, of varying colors (black, brown, red, etc.). Apart from the skin surface of the body, a CMN may occur inside the mouth, on the palms and soles, and even on the scalp
  • The size of CMN can vary from small to large, and based on this, Congenital Melanocytic Nevi are generally classified as:
    • Small Congenital Melanocytic Nevus, with a diameter less than 1.5 cm
    • Medium Congenital Melanocytic Nevus, with a diameter between 1.5 to 19.9 cm
    • Giant or large Congenital Melanocytic Nevus, with a diameter greater than 20 cm
  • There are various types of Congenital Melanocytic Nevi and these include:
    • Café-au-lait macule
    • Garment nevus
    • Halo phenomenon
    • Satellite lesions
    • Speckled lentiginous nevus
    • Tardive nevus
  • The cause of Congenital Melanocytic Nevus is generally unknown, but their formation occurs during the embryological phase of development (while the baby is in the womb). Research studies have implicated certain genetic mutations as being the probable cause
  • Surgical treatment is generally not required for Congenital Melanocytic Nevus unless it presents cosmetic issues, or the lesions are large. Giant CMN has an increased risk for associated malignant melanoma. These moles need to be closely monitored and/or treated
  • The prognosis of Congenital Melanocytic Nevus is generally excellent in most cases, since these nevi are typically benign. Recurrence following treatment may be noted in some cases

Who gets Congenital Melanocytic Nevus? (Age and Sex Distribution)

  • The incidence of Congenital Melanocytic Nevus depends on the size of the nevus:
    • 1 in every 100 children is reported to have a small pigmented lesion at birth (small CMN)
    • 1 in every 1,000 children may have a medium-sized CMN
    • The presence of a giant CMN is estimated at an incidence of 1 in every 20,000 children
  • Both males and females are affected and there is no gender bias observed
  • All racial and ethnic groups are at risk and no predilection is noted

What are the Risk Factors for Congenital Melanocytic Nevus? (Predisposing Factors)

The risk factors for Congenital Melanocytic Nevus have not been clearly identified. However, an association of large CMN with the following have been noted:

  • Neurofibromatosis, a rare genetic disorder with a familial inheritance pattern
  • Presence of other nevi/moles
  • Spinal cord defects at birth, such as spina bifida
  • Lipomatosis, or the presence of multiple lipomas (benign tumor of fat cells)

Note: A family history of CMN is not definitely proven to be a risk factor.

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Congenital Melanocytic Nevus? (Etiology)

The cause of formation of Congenital Melanocytic Nevus is presently unknown.

  • Per studies, during early fetal growth and development, certain morphological errors result in the proliferation of melanoblasts (cells that are precursors to melanocytic cells)
  • This may occur during the first or second trimester (between weeks 5-25), due to genetic abnormalities that may involve proto-oncogenes c-met and c-kit. Proto-oncogenes are mutated genes that may lead to cancer development
  • It is reported that the earlier the overgrowth/proliferation of melanoblast cells take place, the larger and deeper will be the nevus that is formed. The later the process occurs, the smaller will be the size of CMN

What are the Signs and Symptoms of Congenital Melanocytic Nevus?

Congenital Melanocytic Nevus may be small at birth, but will continue to grow in size as the child grows. Since, various parts of the body grow proportionally to different sizes (i.e., hands and legs grow much larger than the head), the size of a fully-grown nevus may be projected by its location on the body.

The signs and symptoms of Congenital Melanocytic Nevus that may be observed include:

  • Usually a solitary nevus is observed on the skin or mucosal surface of the body; these moles/nevi are usually round or oval; although larger nevi can be of any shape
  • New nevi may form following birth, and there may be multiple nevi as the child grows. Some are seen to occur as satellites around a larger lesion
  • Generally, small nevi are asymptomatic and present no pain; but, larger nevi may present dryness of skin (due to abnormal sweat gland function) and increased itchy sensation
  • Small-sized nevi are usually well-defined and evenly pigmented, while larger ones may be irregular in shape and non-uniform in pigmentation
  • The texture of the nevus (especially large ones) may be creased/wrinkled, loose-skinned, or even lumpy
  • The dry skin on a nevus is generally weak; it is more prone to cracking and ulceration
  • There may or may not be the presence of hair on the skin surface of the mole; some may present excess hair (a condition known as hypertrichosis)
  • Certain growth characteristics of the nevus may be more pronounced during puberty, due to hormonal influence. This may be manifested as:
    • Increase in size
    • Projection from the surface of the skin (domical appearance)
    • Increased pigmentation
    • Rapid hair growth on or around the nevus
  • Congenital Melanocytic Nevi can be present as a macule, papule, or plaque
    • Papule: A papule is an area of abnormal skin tissue that is less than 1 centimeter around. Usually a papule has distinct borders, and it can appear in a variety of shapes
    • Macule: A macule indicates the presence of a flat, distinct, discolored area of skin less than 1 cm wide. A macule usually does not involve any change in the thickness or texture of the affected skin
    • Plaque: It is a broad, raised area on the skin. A skin plaque is usually broader than it is high
  • The pigmentation may vary from skin color to red/pink, brown, or black
  • Most nevi are observed on the shoulders, back, chest, abdomen, limbs, and head and neck region. Infrequently, they may be present in the oral cavity, on the head/scalp, and even on the palms of the hands and soles of the feet

How is Congenital Melanocytic Nevus Diagnosed?

A Congenital Melanocytic Nevus is diagnosed through the following tools:

  • Complete physical examination with evaluation of medical history; a simple visual exam can help identify the presence of a nevus
  • Dermoscopy: It is a diagnostic tool where a dermatologist examines the skin using a special magnified lens
  • Wood’s lamp examination: In this procedure, the healthcare provider examines the skin using ultraviolet light. It is performed to examine the change in skin pigmentation
  • Skin biopsy: A skin biopsy is performed and sent to a laboratory for a pathological examination. The pathologist examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis


  • In many cases, no biopsy is necessary. They may be performed to rule out other conditions presenting similar signs and symptoms
  • Some CMN that are biopsied, may present atypical features on examination under a microscope by a pathologist; this may raise the suspicion of a melanoma (a type of skin cancer)

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Congenital Melanocytic Nevus?

There are frequently no complications observed due to a small Congenital Melanocytic Nevus, apart from cosmetic concerns. Medium and usually large CMN may present the following complications:

  • Scratching or itching of the moles may lead to bleeding and ulceration. This can cause secondary bacterial or fungal infections to develop
  • Malignant melanomas have been associated with congenital melanocytic nevi (1-2% risk). Nevertheless, they (the CMN) are not believed to be premalignant lesions
  • The risk for melanoma development is increased with giant nevi. It is estimated that there is a 6-10% risk of melanoma occurrence at the site of the nevus
  • Some children with giant CMN are seen to have an associated neurological abnormality (such as neurocutaneous melanocytosis), affecting the brain and spinal cord
  • Severe emotional and psychological stress due to self-image issues, disfigurement, and social ostracism
  • Scarring of skin following treatment
  • Recurrence of the nevi; in some cases, multiple surgeries may be necessary

How is Congenital Melanocytic Nevus Treated?

The treatment measures for Congenital Melanocytic Nevus may include:

  • The healthcare provider may choose to regularly observe the nevus/mole, to check for any atypical features (a “wait and watch” approach may be followed)
  • Topical applications and skin moisturizers may be used for itching/burning sensations, or for dry skin
  • Surgical excision and removal of the nevus: In many cases, a surgical intervention is not necessary. However, it may be considered in case of cosmetic reasons, or for large CMN presenting a potential risk for melanoma
  • Some superficial skin lesions may be removed through laser therapy
  • Benign nevi can also be excised through surgical procedures
  • Psychological therapy to handle anxiety and stress

How can Congenital Melanocytic Nevus be Prevented?

Current medical research has not established a method of preventing the occurrence of Congenital Melanocytic Nevus.

What is the Prognosis of Congenital Melanocytic Nevus? (Outcomes/Resolutions)

In a majority of cases, the prognosis of Congenital Melanocytic Nevus is excellent, since it is a benign condition. The prognosis is excellent, even if no treatment is provided and only periodic observation maintained in most individuals.

  • Current research does not indicate that there is a significant risk for the formation of malignant melanoma from small-sized congenital melanocytic nevi
  • However, larger nevi have a higher risk for melanoma development. In such cases, the prognosis may be assessed on a case-by-case basis

Additional and Relevant Useful Information for Congenital Melanocytic Nevus:

  • Do not pick or scratch the moles
  • It is important to note that a congenital melanocytic nevus does not become a melanoma with scratching, itching, or trauma. However, these should be avoided since bleeding and ulceration of skin may cause superimposed infections
  • If a mole is present at birth, it is referred to as a congenital mole. If they occur in the first 2 years of life, some healthcare providers call them congenital-type moles

What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

Helpful Peer-Reviewed Medical Articles:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Feb. 10, 2017
Last updated: June 16, 2022