Skin Cancer Home > The ABCDE Signs of Skin Cancer: "B" Is for Border Irregularity

Most moles are noncancerous and appear with uniform, smooth edges. However, a mole that has uneven, ragged, or "blurred" edges could be a sign of skin cancer. By checking your skin on a monthly basis, learning how many moles you have, where they are, and what they look like, you can help detect -- and even prevent -- skin cancer.

Skin Cancer vs. Normal Mole

If you notice a dark spot or mole on your skin, it doesn't automatically mean it is skin cancer. However, knowing how to tell the difference between a "good" mole and a potentially cancerous mole is important to prevent serious skin problems.
A mole is a common, noncancerous growth that occurs in the pigment (color) cells of the skin called melanocytes. Moles generally appear in the first year of life and usually peak in number by the time a person is in his or her 20s or 30s. By this age, the average number of moles a person will have is generally around 25. However, this number may be higher if the skin has had significant sun or ultraviolet (UV) exposure.
The number of moles you have is a strong indicator of your risk for developing melanoma, the most dangerous form of skin cancer. For instance, if you have over 100 moles on your body, you have a higher risk of developing melanoma than someone who has only 25 moles.
Melanoma is a type of cancer that originates in the melanocytes. Although these moles are usually black or dark brown, they can also be pink, red, purple, blue, or white. There are other distinguishing features that set cancerous moles apart from normal moles. These differences are included in the ABCDE signs of skin cancer prevention, with the following meanings for the acronym:
  • A for asymmetry -- one half of a mole does not match the other
  • B for border irregularity -- the edges are irregular, notched, or blurred
  • C for color -- the color is not the same all over and may include shades of brown or black, or sometimes with patches of pink, red, white, or blue
  • D for diameter -- the spot is larger than 6 millimeters across (about ¼ inch -- the size of a pencil eraser), although melanomas can sometimes be smaller than this
  • E for evolving -- the mole is changing in size, shape, or color.
Although all of these signs are possible red flags for melanoma, this article is going to focus on "B" for border irregularities.
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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