What are moles?

Moles are common skin lesions. Moles 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.

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 moles 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, ie, their appearance under the microscope (dermatopathology). They are described according to the site of the naevus cells in the skin.

Junctional naevi

Junctional naevi have groups or nests of naevus cells at the junction of the epidermis (outer layer of the skin) and the dermis (inner layer). These tend to be flat colourful moles.

Dermal naevi

Dermal or intradermal naevi have naevus cell nests in the dermis. These moles are thickened and often protrude from the skin surface (papillomatous naevi). They may be pigmented or skin-coloured.

Compound naevi

Compound naevi have nests of naevus cells at the epidermal-dermal junction as well as within the dermis (compound naevi). These moles have a central raised area and may be surrounded by flat pigmentation.

Moles - Images Copyright DermNet (NZ)

Junctional naevus	Dermal naevus

Dermoscopy classification of melanocytic naevi

A new classification of melanocytic naevi relies on their appearance on dermoscopy, a technique used by dermatologists to evaluate the structure of moles using a hand-held magnification device.

Dermoscopic patterns of melanocytic naevi include:

• reticular naevi
• globular naevi
• blue naevi
• starburst naevi
• site-related naevi
• naevi with special features
• unclassifiable naevi .

Terminology used to describe moles

Dermatologists and pathologists have given a variety of names to moles.

Congenital pigmented naevus

Congenital melanocytic naevi include:

• giant or bathing trunk naevus
• café au lait macule
• speckled lentiginous naevus or naevus spilus
• naevus of Ota and naevus of Ito
• Mongolian spot.

Acquired melanocytic naevus

Ordinary moles that appear after birth may be referred to as 'common acquired naevi'. They are often a solid pink, tan, dark brown or blackish colour; darker colours are more typically found in those with darker skin types.

Acquired melanocytic naevi also include less common variants:

• Atypical naevus; this term is often used to mean any 'funny-looking' mole. However, some dermatologists use atypical naevus to describe a mole that is large (bigger than 5mm) and has ill-defined or irregular borders, varying shades of colour, as well as flat and bumpy components. This type of mole is also called a Clark naevus.
• Dysplastic naevus is sometimes used as another name for atypical or Clark naevus. However, the term dysplastic naevus is best used by a pathologist to describe a mole with specific microscopic criteria.
• Blue naevus, a special deeply pigmented type of dermal naevus
• Halo naevus or Sutton naevus, in which there is a white halo around a mole that gradually fades away
• Spitz naevus or epithelioid cell naevus, a pink dome-shaped mole that arises in children and young adults
• Reed or spindle cell naevus, a dark-coloured variant of Spitz naevus
• Meyerson naevus, a naevus affected by eczema/dermatitis
• Cellular naevus, a non-pigmented dermal naevus
• Unna naevus, a papillomatous dermal naevus that is in the shape of a raspberry
• Cockade or naevus en cocarde/cockarde, in which there is a central dark naevus surrounded by concentric circles of light and dark pigmentation like a rosette
• Fried-egg naevus, a compound naevus with a flat rim of pigment around a bumpy central portion – the bump can be lighter or darker than the pigmented rim
• Eclipse naevus, which has a ring, or segment of a ring, of darker pigment around a tan or pink centre
• Lentiginous naevus, a small, dark brown or black, flat lesion, often with a slightly paler rim – people with multiple lentiginous naevi have been said to have 'cheetah' phenotype
• Combined naevus, with two distinct types of mole within the same lesion – these include common naevi, blue naevi, blue naevi, and Spitz naevi
• Recurrent naevus, or reappearance of pigment in a scar following surgical removal of a mole – this may have an odd shape.

Signature naevi

Signature naevi are defined as the predominant group of naevi in an individual. They share clinical characteristics. For example, many are solid brown or pink moles, or the eclipse, cockade or fried-egg types described above.

Freckles

Freckles are small, pale brown flat marks, more common in fair-skinned individuals, especially those with red hair and blue eyes. Freckles occur in sun-exposed areas of skin, and are darker and more numerous during the summer months. Most freckles are due to localised increased production of melanin pigment rather than due to increased numbers of melanocyte cells.

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 [detailed examination of the skin surface using a magnification device].

It is not always possible to tell whether the lesion is a melanoma just by 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 ducking' 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.

Shave biopsy

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 (eg. 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

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 only be removed permanently by electrolysis, laser, or excision of the whole mole.

Skin examinations

• Perform a skin self-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 and/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 scanning.

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 and 5pm.
• Apply sunscreen to areas you can't cover. Choose broad spectrum high protection (SPF 30+) sunscreens, applied frequently to exposed areas.

Original material provided by the New Zealand Dermatological Society Inc. (DermNet NZ), February 2010, and reviewed by everybody, August 2010.