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# Melanocytic nevi and dysplastic nevus

Moles are common, harmless clusters of pigment cells. Atypical (dysplastic) moles look irregular and mark a higher risk of melanoma, so changes need checking.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Skin](https://durgical.com/en/anatomy/skin/)

## Why it happens

- [Oncogenes: RAS, MYC, HER2, BCR-ABL and the table to know](https://durgical.com/en/general-pathology/oncogenes-ras-myc-her2-bcr-abl-and-the-table-to-know/)
- [Tumour suppressor genes: RB, TP53, APC, BRCA and the two-hit hypothesis](https://durgical.com/en/general-pathology/tumour-suppressor-genes-rb-tp53-apc-brca-and-the-two-hit-hypothesis/)
- [Keratinocytes, melanocytes, Langerhans and Merkel cells](https://durgical.com/en/histology/keratinocytes-melanocytes-langerhans-and-merkel-cells/)

## What it is

Benign proliferations of melanocytes (naevus cells) in the epidermis, dermis or both, appearing as round, evenly coloured brown or skin-coloured macules or papules. Dysplastic (atypical) naevi are larger and more irregular in shape and colour; they rarely turn into melanoma themselves but are markers of increased melanoma risk.

## Who gets it

Almost everyone has moles; adults typically have 10–40. Most appear in childhood and up to about age 40 and many fade in old age. About 1 in 10 people has at least one dysplastic naevus. Light-skinned people have more naevi; in darker skin, as in much of Colombia, naevi and melanomas on the palms, soles and nails (acral) are relatively more important.

## Causes

- Benign clonal proliferation of melanocytes, often driven by BRAF (acquired naevi) or NRAS (congenital naevi) mutations
- Genetic predisposition: number of naevi is strongly inherited; familial atypical multiple mole melanoma (FAMMM) syndrome with CDKN2A mutations
- Sun exposure in childhood increases the number of acquired naevi

## Risk factors

- Fair skin, light hair and eyes, tendency to burn
- Intermittent intense sun exposure and blistering sunburns in childhood
- Family history of many or atypical moles or of melanoma
- Immunosuppression
- Melanoma risk rises with more than 50 common naevi, any dysplastic naevi, or a large congenital naevus

## Pathophysiology

A growth-promoting mutation (usually BRAF V600E) makes melanocytes proliferate into nests, then a protective program called oncogene-induced senescence stops their growth, so most naevi stay stable for life. Naevi evolve from junctional (nests at the dermoepidermal junction, flat and dark) to compound (junction and dermis, slightly raised) to intradermal (dermis only, dome-shaped, often skin-coloured). Additional mutations (for example CDKN2A, TERT, PTEN) can bypass senescence and lead to melanoma; dysplastic naevi have some of these changes and show architectural and cytological atypia.

## Classification

- By depth: junctional, compound and intradermal naevi
- Congenital naevi: small (20 cm adult size); giant ones carry higher melanoma risk
- Dysplastic (atypical, Clark) naevus
- Special types: blue naevus, halo naevus, Spitz naevus

## Symptoms and signs

- Common naevus: small (usually 6 mm, flat with a raised centre ('fried egg'), irregular or blurred border, mixed tan, brown and pink colours
- Most common on sun-exposed trunk and limbs; dysplastic naevi often on the back
- Usually no symptoms

## Red flags

- ABCDE changes: Asymmetry, irregular Border, several Colours, Diameter >6 mm, Evolution (change in size, shape, colour or elevation)
- 'Ugly duckling' lesion that looks different from the patient's other moles
- New pigmented lesion after age 40, or a mole that itches, bleeds or ulcerates
- Dark band in a nail or a growing pigmented lesion on the palm or sole (acral melanoma, important in Latin America)

## Diagnosis

**Clinical**
Full- [skin](https://durgical.com/en/anatomy/skin/) examination in good light, including scalp, palms, soles, nails and mucosa; apply the ABCDE rule and the 'ugly duckling' sign. Dermoscopy improves accuracy (regular network or globular pattern in benign naevi).

**Tests**
Excisional biopsy with narrow margins of any suspicious lesion for histopathology, which is the only way to confirm or exclude melanoma; partial biopsies of suspicious pigmented lesions are avoided when possible. High-risk patients may have total-body photography and sequential digital dermoscopy.

**Imaging**
Not needed for naevi; MRI of brain and [spine](https://durgical.com/en/anatomy/region/spine/) for a large congenital naevus over the spine or head (neurocutaneous melanosis).

## Differential diagnosis

- Melanoma
- Seborrheic keratosis
- Solar lentigo and freckles (ephelides)
- Pigmented basal cell carcinoma
- Dermatofibroma and haemangioma

## Goal of treatment

Recognise and remove lesions suspicious for melanoma early, educate on self-examination and sun protection, and avoid unnecessary removal of benign moles.

## Treatment

**Conservative**
Typical benign moles need no treatment; explain that removing all atypical moles does not prevent melanoma.

**Surgical**
Complete excision with narrow margins and histology of changing or suspicious lesions; re-excision of moderately or severely dysplastic naevi with positive margins as advised by pathology.

**Follow-up**
Regular skin examinations (more often in people with many or dysplastic naevi or a family history of melanoma), dermoscopic follow-up and monthly self-examination with photographs.

**Lifestyle**
Sun protection: shade, protective clothing, broad-spectrum sunscreen, avoiding tanning beds, especially in children.

## Complications

- Melanoma, either arising in a naevus (minority of melanomas) or elsewhere in high-risk patients
- Irritation, inflammation or bleeding from trauma
- Scarring after excision
- Neurocutaneous melanosis with giant congenital naevi

## Prognosis

Common naevi are benign and stable; the lifetime risk of any single mole becoming melanoma is very low. People with many or dysplastic naevi have a several-fold higher melanoma risk and benefit from surveillance; most melanomas found early are curable by excision.

## Prevention

- Sun protection from early childhood and avoiding sunburn
- Avoid tanning beds
- Monthly self-examination of the skin, including palms, soles and nails
- Skin checks for relatives of people with melanoma

## Test yourself

Think of the answer, then tap the question to see it.

## What does the ABCDE rule stand for?

Asymmetry, Border irregularity, Colour variation, Diameter >6 mm and Evolution (change).

## Is a dysplastic naevus a premalignant lesion that must always be removed?

It rarely becomes melanoma itself; it mainly marks increased melanoma risk. Removal is for changing or suspicious lesions, plus surveillance.

## What is the 'ugly duckling' sign?

A mole that looks different from the patient's other moles, which raises suspicion for melanoma.

## Which biopsy is preferred for a lesion suspicious for melanoma?

Complete excisional biopsy with narrow margins for histopathology.

## Which gene mutation is most common in acquired naevi?

BRAF (V600E).

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## Related conditions

- [Melanoma](https://durgical.com/en/conditions/melanoma/)
- [Seborrheic keratosis](https://durgical.com/en/conditions/seborrheic-keratosis/)
- [Basal cell carcinoma](https://durgical.com/en/conditions/basal-cell-carcinoma/)
- [Vitiligo](https://durgical.com/en/conditions/vitiligo/)
- [Infantile hemangioma](https://durgical.com/en/conditions/infantile-hemangioma/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Moles](https://medlineplus.gov/moles.html) (MedlinePlus, US National Library of Medicine, 2026); [Common Moles, Dysplastic Nevi, and Risk of Melanoma](https://www.cancer.gov/types/skin/moles-fact-sheet) (National Cancer Institute, 2026).

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Source: https://durgical.com/en/conditions/melanocytic-nevi-and-dysplastic-nevus/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/melanocytic-nevi-and-dysplastic-nevus/