What are moles?

Melanoma care with Northwestern Medicine Dermatology

Moles are clusters of pigmented cells that are often dark brown or black. Most moles are harmless and vary in shape and size, and some may even change shape and size without becoming cancerous. Moles that become painful, itch, bleed, or suddenly become asymmetrical, or change size, shape or color should be looked at by a dermatologist. Moles are more likely to become cancerous if they are large or atypical or if the patient has numerous moles.

Talk to your dermatologist if you are concerned about a new or changing mole or if you are at high risk for skin cancer.

Warning Signs to Identify Melanoma

ABCDE warning signs can help you identify spots that may be melanoma:1

  • Asymmetry. Moles with sides that do not match.
  • Border that is irregular. Moles that lack smooth and uniform edges.
  • Color changes. Moles that are not black or brown or that contain 3 or more colors.
  • Diameter. Moles that are greater than 6 millimeters (about ¼ inch).
  • Evolving. Moles that change shape, color or size over time.


  1. Rigel DS, Friedman RJ, Kopf AW, Polsky D. ABCDE—an evolving concept in the early detection of melanoma. Archives of dermatology. 2005;141(8):1032-1034.