Nevus (Mole): Medical Definition, Types & Monitoring

Definition

A nevus (plural: nevi) is a benign proliferation of melanocytes (pigment-producing cells). Commonly called a mole.

Classification

Type	Onset	Features	Risk
Congenital Melanocytic Nevus	Birth / <1 yr	Variable size; giant (>20 cm) → melanoma risk ~5%	Low–moderate
Acquired Melanocytic Nevus	Childhood–adulthood	Junctional, compound, dermal; <6 mm, symmetric, uniform color	Very low
Dysplastic (Atypical) Nevus	Adolescence+	>5 mm, irregular borders, color variegation; familial (FAMMM syndrome)	Increased (marker + precursor)
Blue Nevus	Any age	Deep dermal melanocytes → blue-black; usually benign	Very low
Spitz Nevus	Children/young adults	Pink/red dome; histologically mimics melanoma	Low (but excise to confirm)

ABCDE Monitoring (Self-Exam)

• Asymmetry
• Border irregularity
• Color variation
• Diameter >6 mm
• Evolution (change in size, shape, color, symptoms)

When to Biopsy

Any lesion meeting ABCDE criteria, new mole after age 30, symptomatic (itch, bleed), or "ugly duckling" (looks different from patient's other nevi).