Freckles, lentigines and melanocytic nevi
- Lesion
Freckles and sun spots are pigment changes; moles are benign clusters of pigment cells. A few atypical moles mark higher melanoma risk.
What it is
Pigmented lesions range from simple increases in melanin to benign tumours of melanocytes. A freckle has more melanin but normal melanocyte numbers; a lentigo has more melanocytes along the basal layer. Melanocytic nevi are benign clonal proliferations, usually driven by BRAF or NRAS mutations that then stop growing through oncogene-induced senescence. Dysplastic nevi show architectural and cytologic atypia and, in families with many of them, mark a high risk of melanoma.
Structure
- Junctional nevus: nests at the dermoepidermal junction; flat, uniformly dark.
- Compound nevus: junctional plus dermal nests; raised.
- Intradermal nevus: dermal nests only, often skin-coloured, dome-shaped.
- Dysplastic nevus: shoulder of junctional component beyond the dermal part, fused (bridging) nests, random atypia, lymphocytes.
- Blue nevus: heavily pigmented dendritic melanocytes deep in the dermis (Tyndall effect gives the blue).
Step by step
- A melanocyte acquires an activating BRAF (often V600E) or NRAS mutation.
- The clone proliferates and forms nests at the junction.
- Strong oncogenic signalling triggers senescence (p16 rise) and growth stops.
- Cells migrate into the dermis and mature.
- If additional hits occur (CDKN2A loss, TERT), atypia and eventually melanoma can arise; most nevi never progress.
Clinical notes
- Most melanomas arise de novo, not from an existing nevus.
- Dysplastic nevus syndrome: many atypical nevi plus family history; close skin surveillance.
- Large congenital nevi carry a small lifetime melanoma risk.
Test yourself
Think of the answer, then tap the question to see it.
What distinguishes a freckle from a lentigo histologically?
A freckle has more melanin with normal melanocyte numbers; a lentigo has an increased number of basal melanocytes.
What is maturation in a melanocytic nevus?
Deeper dermal nevus cells become smaller, less pigmented and more neural-like; its absence suggests melanoma.
Why do most nevi stop growing despite a BRAF mutation?
Strong oncogenic signalling induces senescence, with p16 and other checkpoint proteins halting the cell cycle.
Elsewhere in DurgiPedia
- Keratinocytes, melanocytes, Langerhans and Merkel cells
- Pigments in tissue: lipofuscin, hemosiderin, melanin, bilirubin, carbon
- Dysplasia and carcinoma in situ
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Moles (MedlinePlus, US National Library of Medicine, 2025); Common Moles, Dysplastic Nevi, and Risk of Melanoma (National Cancer Institute, 2025); Skin Pigmentation Disorders (MedlinePlus, US National Library of Medicine, 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.