16/02/2026
A congenital melanocytic nevus (CMN) is a benign, pigmented skin lesion (mole) present at birth or appearing shortly after, caused by genetic mutations (often NRAS) during fetal development. Ranging from small to giant (
cm), these moles can grow, change color, or develop hair. While mostly harmless, large CMNs carry an increased, albeit low, risk of malignant melanoma.
Causes and Risk Factors -
Genetic Mutation: They are caused by sporadic, postzygotic mutations (not inherited) that affect the proliferation and migration of melanocytes between weeks 5 and 21 of gestation.
Prevalence:
They occur in approximately 1% of newborns worldwide.
Symptoms and Characteristics
Appearance: Tan to black or bluish, sometimes with uneven borders, and often develop excess hair (hypertrichosis).
Texture: Surfaces can be flat, rough, raised, or bumpy.
Growth: They generally grow at the same rate as the body.
Location: Can appear anywhere, but often on the trunk or limbs.
Associated Issues:
The skin may be thin, dry, and prone to irritation or itching.
Prognosis and Risks
Melanoma Risk: While the risk of malignancy in small CMNs is low, large or giant CMNs carry a higher risk of developing melanoma.
Neurocutaneous Melanosis (NCM): In rare cases, especially with large/multiple nevi, pigment cells can be present in the brain and spinal cord, which can be fatal if it becomes symptomatic.
Appearance Changes: CMNs often lighten over time, matching the patient's skin tone more closely as they grow.
Treatment
Observation: Many small to medium nevi require no treatment, only regular monitoring.
Surgery: Surgical excision is the primary treatment for large nevi to reduce the risk of malignancy and for cosmetic improvement.
Not Recommended: Superficial treatments like laser, dermabrasion, and curettage do not permanently remove the nevus, can cause scarring, and are not recommended.
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