Moles or Nevi commonly appear throughout the first four decades of life. After this time any new mol…
What are nevi?
Nevi are benign growths of melanocytes which are the cells which produce melanin, the pigment in the skin.
What causes nevi?
The critical events which lead to the development of nevi remain a mystery. Exposure to ultraviolet radiation and genetic factors both play a role. There appears to be a variable relationship between the tendency to sunburn and freckle, and the development of nevi.
When do nevi appear?
The majority of develop throughout the second and third decades of life although some may appear in the first 6 to 12 months of life. Not uncommonly, nevi may also be present at birth (congenital nevi) but these seem to be different from those acquired after birth. They occur equally in both males and females.
What happens to nevi in the course of a lifetime?
Generally, an individual naevus grows slowly over many years and ultimately attains its full size and then remains stable for decades. Eventually, many nevi regress such that only a few true moles are present in the 7th and 8th decades. As we age, new nevi are rare and that is why a growing lesion in an adult has a greater risk of being melanoma. Sometimes the body’s own immune system “attacks” a mole. An area of depigmentation (whitening) occurs around the mole and ultimately the mole may disappear.
How many moles are considered normal?
There is a huge range as to what is considered a normal number of moles. In studies of fair skinned Australians, in the third decade of life, the average number of moles per person is 35.
Is there a typical appearance for a mole?
No. Appearances vary considerably, but in general they appear “orderly” with even surface and colour, round or oval in shape, with regular edges and relatively sharp borders. They may be dome shaped or flat topped, fully flat or warty or fleshy or appear to be growing on a stalk. They may be flesh coloured, pink or brown. More elevated nevi tend to be more lightly pigmented, flatter nevi tend to be darker in colour.
Very dark brown and black are unusual colours in nevi in lightly coloured skins, but are common colours in darkly pigmented skins. Blue grey, red and white are in nevi are not typical and ought to be viewed with suspicion.
Nevi may grow hair which may be coarser, longer and darker than in surrounding skin.
What is the significance of a large number of nevi?
Multiple studies demonstrate an increased melanoma risk in individuals with a large number of nevi. For example, in patients with 100 or more nevi, the risk is 3 times greater risk compared to those with fewer than 25 nevi. The relative risk is 12 times more for patients with 10 or more dysplastic nevi. In patients with numerous nevi, (and/or dysplastic nevi) the nevi themselves are best viewed as a marker of increased melanoma risk, not as precursors or pre-cancers of melanoma.
What is the risk of a mole becoming malignant?
No one knows what the risk of an individual mole becoming malignant might be. Suffice to say, a mole with a normal clinical appearance has a very low risk overall. However, a changing mole, especially if it has atypical clinical features, has a much higher risk. This is why changing moles should always be checked by a Doctor.
Should all moles be treated?
Absolutely not, because the vast majority of moles are harmless. Patient with numerous nevi, especially dysplastic nevi, and a personal for family history of melanoma should be screened regularly for life.
Moles may be treated for cosmetic reasons, because they are being recurrently traumatised or because there are suspicious features. In the latter scenario, complete excision is recommended so that full microscopic analysis can be performed. Clinically suspicious moles must never be treated with liquid nitrogen, diathermy, dermabrasion or laser.
It is acceptable to shave clinically benign lesions for cosmetic reasons as this procedure is associated with much less scarring. However, a pathology check is always advised.
Can moles be prevented?
Possibly, but only through a comprehensive sun protection programme commencing in early childhood.