A nevus is also called a mole. Some moles are present at birth (a congenital nevus), and some may develop later in childhood and adulthood (an acquired nevus). They can develop on any part of the body and may look different depending on the body location.
Moles vary widely in appearance and size. They can range from the size of a small pin-point spot to several centimeters in some cases. In very rare cases, moles can take up half of the body’s surface area. They can be flat or bumpy. Their color may vary from skin-colored to pink to light brown, dark brown, steel blue or black. They can have many shapes such as round and oval or irregular star or square formations. Some moles may have hair growing out of them. Most moles are benign (not cancerous). Every so often, moles can have atypical appearances (irregular shape, borders, and color), may change rapidly (over days to weeks), and/or become bothersome (itch, bleed, etc.). These features may suggest that the moles are developing into melanomas.
The exact cause for moles is not known. It is likely due to a combination of genetic factors, the function of the immune system, and sun exposure for the following reasons:
- People who have many moles tend to have family members who also have many moles.
- Some inherited genetic mutations can cause one to be born with moles.
- Medications used to fight cancers and that weaken the function of the immune system may cause darkening of existing moles or development of new moles.
- Sun exposure plays a role in the development of moles. A study in children showed that having a previous sunburn or sun sensitivity is associated with developing more moles.
Acquired moles may be prevented by sun protection and sunscreen use. Since most moles are benign, they do not need to be treated unless they become painful, itchy, or bleed when injured.
A qualified health professional should evaluate moles carefully to check for irregularity. In adults, a rule of thumb is the ABCDE rule:
A = Asymmetry: check to see if a mole looks asymmetrical.
B = Border: check to see if the mole has regular borders and note that sometimes a mole can have irregularities along the border.
C = Color: check to see if the mole has even color.
D = Diameter: moles can come in many different sizes but if a mole is large and growing, it should be evaluated.
E = Evolution: if a mole is changing in size, color, shape, or its border, it should be evaluated.
Studies have shown in children, the ABCDE rule should be modified so that it also includes additional ABCD criteria for children as follows:
A = Amelanotic: Bumps in children that look pinkish rather than black or brown.
B = Bleeding: Lesions that are bleeding.
C = Color: In children, moles that are uniform in color should still be evaluated by a health professional.
D = De novo for any diameter: new moles of any size in children should be evaluated.
A dermatologist should evaluate any concerning moles and determine if it should be biopsied and discuss how this can be performed. A dermatologist may decide to remove a mole by using one of several different methods:
- Punch biopsy
- Shave removal
1. Satagopan JM, Oliveria SA, Arora A, et al. Sunburn, sun exposure, and sun sensitivity in the Study of Nevi in Children. Ann Epidemiol.2015;25(11):839-843; PMID: 26096189.
2. Cordoro KM, Gupta D, Frieden IJ, et al. Pediatric melanoma: results of a large cohort study and proposal for modified ABCD detection criteria for children. J Am Acad Dermatol.2013;68(6):913-925; PMID: 23395590.