What is a mole?
Moles are common skin lesions. They are correctly called melanocytic naevi (American spelling ‘nevi’), as they are due to a proliferation of the pigment cells, melanocytes. If they are brown or black in colour, they may also be called pigmented naevi. Moles are benign in nature (harmless), but a malignant melanoma (cancerous mole) may arise within a mole.
Naevi may form from other skin cells (e.g. vascular naevi are formed from blood vessels), but only those derived from melanocytes are known as moles.
What do moles look like?
Moles may be flat or protruding. They vary in colour from pink or flesh tones to dark brown or black. Although mostly round or oval in shape, they are sometimes unusual shapes. They range in size from a couple of millimetres to several centimetres in diameter.
The number of moles a person has depends on genetic factors and on sun exposure; most white-skinned New Zealanders have 20-50 of them. People with a greater number of moles have a higher risk of developing melanoma than those with few moles, especially if they have over 100 of them.
When do they appear?
One or more moles may be present at birth. These brown birthmarks are more correctly known as congenital melanocytic naevi. If birthmark-like moles appear within the first two years of life, they are sometimes called 'congenital-type' melanocytic naevi.
More frequently moles arise during childhood or early adult life, when they are called acquired melanocytic naevi. Exposure to sunlight increases the number of moles. Teenagers and young adults tend to have the greatest number of moles and there are fewer in later life because some of them slowly fade away.
Classification of melanocytic naevi
The conventional classification of melanocytic naevi depends on light microscopy i.e. their appearance under the microscope (dermatopathology). They are described according to the site of the naevus cells in the skin. Pathologists may also describe congenital melanocytic naevi as superficial (Ackerman naevus), deep (Zitelli naevus) or combined.
|Reticular naevus||Globular naevus||Blue naevus||Starburst naevus|
|Reticular naevus reveal a lattice of intersecting brown lines.||Globular naevus characteristically show aggregated brown oval structures.||The blue naevus is a uniform structureless lesion, steel-blue in colour.||Starburst naevus reveals radial lines around periphery of lesion.|
|Site-related naevus: facial||Site-related naevus: acral||Naevus with special features||Unclassifiable naevus|
|Facial naevi reveal pseudonetwork around hair follicles||Acral naevi (these are on palms and soles) tend to be made up of parallel lines.||Naevi with special features include eczematised naevus (illustrated), irritated naevi and halo naevi.||The unclassifiable naevus doesn't have any of the other patterns.|
Terminology used to describe moles
Dermatologists and pathologists have given a variety of names to moles.
Congenital pigmented naevus
Congenital melanocytic naevi are those present at birth (true congenital naevi) or arising soon afterwards (congenital-like or tardive naevi).
|Small congenital naevus||Medium congenital naevus||Giant naevus||Hairy congenital naevus|
|Small congenital naevi are less than 1.5 cm diameter.||Medium congenital naevi are 1.5 to 10 cm diameter.||The giant, or bathing trunk naevus, is larger than 20 cm.||Hairy congenital naevi grow thick long hairs.|
|Café au lait macule||Speckled lentiginous naevus||Naevus of Ota||Mongolian spot|
|Café au lait macule is a flat brown patch.||Speckled lentiginous naevus is a flat brown patch with darker spots.||Naevus of Ota is a bluish brown mark around forehead, eye and cheek.||Mongolian spot is a large bluish mark most often seen on buttocks of newborn.|
Acquired melanocytic naevus
Ordinary moles that appear after birth may be referred to as acquired naevi. They are often a pink, tan, dark brown or blackish colour; darker colours are more typically found in those with darker skin types. Acquired melanocytic naevi are given a variety of names and there is considerable overlap of descriptions.
Naevi may be described as typical or atypical (not typical). Typical moles affect nearly everyone. The term atypical naevus is often used to mean any funny-looking mole. However, some dermatologists use atypical naevus to describe a mole with specific characteristics: large (>5 mm); ill-defined or irregular borders; varying shades of colour; with flat and bumpy components. This type of mole is also called a Clark naevus. They usually occur in fair skinned individuals and may be solitary or numerous.
|Common naevus||Naevus in dark skin||Atypical naevus||Dysplastic naevus|
|A common naevus is a flat mole with a single uniform colour.||In dark skin, naevi are often black in colour.||People with multiple atypical naevi are at increased risk of melanoma (cancerous mole).||Dysplastic naevus describes an atypical mole that has specific microscopic criteria.|
|Blue naevus||Cellular naevus||Miescher naevus||Unna naevus|
|Blue naevus is a deeply pigmented type of dermal naevus.||Cellular naevus is a non-pigmented dermal naevus.||Miescher naevus is a dome-shaped smooth dermal naevus often found on the face.||Unna naevus is a papillomatous dermal naevus that is in the shape of a raspberry.|
|Meyerson naevus||Halo naevus||Spitz naevus||Reed naevus|
|Meyerson naevus is a naevus affected by a halo of eczema/dermatitis.||Halo naevus or Sutton naevus has a white halo around the mole. The mole gradually fades away over several years.||Spitz naevus or epithelioid cell naevus, is a pink (classic Spitz) or brown (pigmented Spitz) dome-shaped mole that arises in children and young adults.||Reed or spindle cell naevus, is a very 5dark-coloured mole with spindle-shaped dermal melanocytes, usually found on the limbs.|
|Recurrent naevus||Agminated naevus||Acral naevus||Nail unit naevus|
|Recurrent naevus refers to the reappearance of pigment in a scar following surgical removal of a mole – this may have an odd shape.||An agminated naevus is a cluster of similar moles or freckles.||Acral naevus refers to one on the palm or sole.||Nail unit naevus causes a uniform longitudinal band of pigment on a nail.|
© Dr Ph Abimelec – dermatologue
Signature naevi are defined as the predominant group of naevi in an individual with multiple moles. They share clinical characteristics and may be typical or atypical.
Change in a mole
In adults, it is wise to take change in a mole seriously. Malignant melanoma is a cancerous growth occurring in melanocytes (pigment cells). At first a melanoma may look similar to a harmless mole, but in time it becomes more disordered in structure and tends to enlarge.
If a mole changes size, shape or colour, or a new one develops in adult life it should be evaluated by a dermatologist or other doctor with skills in the recognition of skin cancer. The dermatologist may examine the mole by dermoscopy. It is not always possible to tell whether the lesion is a melanoma just be looking at it, so if there is any doubt it may be necessary to cut the mole out for pathological examination.
Removal of moles
Although most moles are harmless and can be safely left alone, moles may be treated under the following conditions:
- Possible malignancy: a mole that has bled, has an unusual shape, is growing rapidly or changing colour. These are sometimes known as 'ugly duckling' moles and may turn out to be melanoma.
- Nuisance moles: a mole that is irritated by clothing, comb or razor.
- Cosmetic reasons: the mole is unsightly.
Treating a protruding mole is simple using a procedure called a shave biopsy. After numbing the skin with local anaesthetic the doctor removes the projecting part of the mole with a scalpel or by electrosurgery (e.g. Surgitron method). The wound heals to leave a flat white mark, but sometimes the colour remains the same as the original mole.
Shave biopsy is sometimes used to remove a flat brown patch or freckle for pathological examination. This is sometimes called saucerisation or tangential excision.
Excision biopsy is necessary if the mole is flat or melanoma is suspected. The full thickness of the skin is removed and the wound is sutured (stitched). The specimen should always be sent to the laboratory for pathological examination (histology). The resulting scar may be just a thin line, but is sometimes more noticeable than the mole was.
The coarse hair that sometimes grows in a mole can be removed by shaving. Plucking may cause inflammation resulting in a painful lump under the mole. The hair can also be removed by electrolysis, laser, or excision of the whole mole.
- Perform a self skin examination monthly: report significant changes in moles or new lesions to your doctor or dermatologist.
- Arrange to have a skin examination regularly if you have numerous moles, atypical moles, previous skin cancer or your doctor recommends this.
- Photographic records can be useful if there are numerous moles &/or atypical naevi. Sophisticated digital mole mapping systems including dermoscopic images are of particular value in the diagnosis of melanoma in people with numerous moles, as subtle changes can be detected on repeat imaging.
Prevention of skin cancer
Sun protection is important to avoid damaging your skin.
- Cover up. Wear a hat, long sleeves and long skirt or trousers. Choose fabrics designed for the sun (UPF 40+) when outdoors in summer between 10am & 5pm.
- Apply sunscreen to areas you can't cover. Choose broad spectrum high protection (SPF 30+) sunscreens, applied frequently to exposed areas.
- Signature nevi. Suh KY, Bolognia JL. J Am Acad Dermatol. 2009 Mar;60(3):508-14. Review. Medline.
On DermNet NZ:
- Atypical naevi
- Halo moles
- Basal cell carcinoma
- Squamous cell carcinoma
- Self skin examination
- Benign melanocytic lesions – common skin lesions course
- Moles – Medline Plus
- Nevus Outreach, Inc.: A non-profit organization dedicated to improving awareness and finding a cure for Congenital Nevi and Neurocutaneous Melanosis.
- MoleMap New Zealand
- Melanocytic nevi – Medscape Reference
- Melanocytic Naevi (Moles) – British Association of Dermatologists
- Grain de beauté – Dr Ph Abimelec website (French)
Books about skin diseases:
See the DermNet NZ bookstore