Natural evolution

Junctional naevus: flat, well-demarcated tan-brown macule; nests of melanocytes confined to the dermo-epidermal junction. Predominantly children and adolescents.
Compound naevus: slightly elevated; combined junctional and dermal melanocyte populations. Young adults.
Intradermal naevus: dome-shaped, often skin-coloured or lightly pigmented; melanocytes entirely within the dermis. Older adults.
Maturation: surface flatness → elevation; pigment loss; hair (terminal); fibrosis. Typical lifecycle 30-40 years.
Total naevus count: peaks 20-30 years; declines from 40 onwards.

Genetics and biology

~80% of common naevi harbour somatic BRAF V600E mutation.
A minority are NRAS-mutant — NRAS is the characteristic driver of congenital naevi.
Single mutation followed by senescence / growth arrest underlies the small size and stability of naevi (unlike melanoma which acquires additional driver mutations).
Heritable factors: total naevus count is heritable; MC1R variants increase number and atypia.

Symmetric in shape, colour, and structure.
Well-demarcated border.
Single dominant colour (light to medium brown typically).
<6 mm diameter usually; can be larger in adolescents.
Stable over time after age 30; concerning if new or changing in adults >40.
Dermoscopy: globular, reticular, homogeneous patterns; symmetric; benign network with regular meshes; centrally hyperpigmented globules.
Hair within naevus does not indicate atypia.

Total naevus count is the strongest single risk factor for melanoma:
- >100 common naevi: relative risk ~7-fold.
- ≥5 atypical / dysplastic naevi: relative risk ~6-fold.
The risk attributable to naevus count is not eliminated by reducing the naevi themselves — surveillance is the appropriate strategy.
UK 2-week-wait NICE NG12 weighted 7-point checklist for melanoma considers changes in pre-existing naevi.
Total body photography / dermoscopy with sequential imaging is NICE NG14-supported for high naevus-count / dysplastic naevus syndrome.

Asymmetry, Border irregularity, Colour variation, Diameter >6 mm, Evolution (ABCDE).
Glasgow 7-point checklist:
- Major (2 points each): change in size, change in shape, change in colour.
- Minor (1 point each): diameter ≥7 mm, inflammation, oozing / crusting / bleeding, change in sensation.
- Score ≥3 → refer.
New naevus appearing in adults >40 years.
"Ugly duckling" — a naevus that looks distinctly different from the patient's other naevi.
Asymmetric dermoscopic features: atypical pigment network, blue-white veil, regression structures, atypical pseudopods / streaks / dots.

Stable, benign-appearing naevi: reassurance + skin self-examination education.
Suspicious naevi: full excisional biopsy with 1-2 mm margin (NICE NG14).
Cosmetic removal: shave excision for elevated intradermal naevi (counsel about pigment / hair regrowth).
Avoid laser / cryotherapy / curettage on pigmented lesions — destroys diagnostic histology.
Surveillance for high-risk patients:
- Naevus count >100, atypical naevus syndrome, familial melanoma, prior melanoma.
- Annual total-body photography ± sequential dermoscopy.
- UV photoprotection counselling.
Counsel: lifelong surveillance; new naevus appearance in adults warrants assessment; ABCDE rule.