Nevus

A localized skin or mucosal lesion caused by an abnormal concentration or growth of cells. Most nevi are benign; common melanocytic nevi are often called moles.

Melanocyte: A pigment-producing cell found mainly in the skin and hair follicles. Melanocytes form the cell population in melanocytic nevi.
Neural crest: An embryonic cell population that gives rise to melanocytes and several other cell types. Melanocytes originate from neural crest cells during development.
Acquired melanocytic nevus: A melanocytic skin lesion that develops after birth, commonly during childhood or adolescence. This is the common acquired mole most often meant by everyday use of “mole.”
Melanoma: A malignant tumor of melanocytes that can invade surrounding tissue and spread to distant organs. Melanoma is the dangerous malignant counterpart considered when a pigmented lesion changes.
Melanin: A group of pigments that gives color to skin, hair, and eyes and helps absorb ultraviolet radiation. Melanin produced by nevus melanocytes contributes to a mole’s color.
Melanocyte migration: The movement of developing melanocytes from the neural crest to their destinations in skin and other tissues. Disrupted migration can leave localized clusters of pigment cells.
Dysplastic nevus: A melanocytic nevus with atypical clinical or microscopic features, sometimes associated with increased melanoma risk. Its atypia can make distinction from melanoma clinically important.
Dermoscopy: A noninvasive examination of skin using magnification and illumination to reveal subsurface structures. It helps clinicians assess pigment patterns when distinguishing nevi from melanoma.
Epidermis: The outermost layer of skin, forming a protective barrier over the body. Some nevi involve cells at the skin’s surface layer.
BRAF: A gene encoding a protein kinase in the RAS–RAF–MEK–ERK cell-signaling pathway. Acquired BRAF mutations are common in acquired melanocytic nevi.

Linked from 3 pages

Post-inflammatory hyperpigmentationCompared with: A nevus is a persistent lesion, not pigment left after inflammation heals.