How Do You Know When a Mole is Cancerous?

How Do You Know When a Mole is Cancerous?
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Moles and Melanomas

Moles are benign growths on the skin that result from a clustering of melanocytes (the cells that produce melanin and are thus responsible for skin pigmentation). The technical term for a mole is nevus. Now, a type of skin cancer called melanoma, is a cancer that starts in the melanocytes, the same cells that give rise to moles. So, moles are risk zones for the development of melanomas. But how do you know when a mole is cancerous?

Risk Factors

Melanoma is a fairly common cancer, affecting 3 to 7% of Western populations, with a slight tendency to affect more women than men. The main risk factor for the development of melanomas is ultraviolet light. Most people come in contact with ultraviolet light mainly through sun exposure. Some risk factors related to this, are:

  • The number of moles: the more moles you have, the higher the chance one of them is ‘bad’.
  • Sun exposure and sunburn both increase the risk.
  • Being very fair skinned also increases the risk, as fair skinned individuals are more sensitive to ultraviolet light.
  • Family history: If there are several cases of melanoma in your family, you run a higher risk of developing one yourself.

Skin Examination

If you are at risk, or even when there is no real indication you are, it might be a good idea to subject yourself to a skin examination every once in a while. This just means that you check your own skin for signs of unusual pigmentation. You should check all body parts, even the scalp, as moles or melanomas might hide between your hair.


A rule dermatologists often use to determine whether a mole could possibly be a melanoma, is known as the ABCD rule (sometimes with an extra feature for identification, making it ABCDE).

  • Asymmetry: Regular moles are entirely symmetrical. So when a mole is no longer a perfectly symmetrical shape, this is an indication it might be skin cancer.
  • Border: A normal mole has a clear and distinct border, whereas cancerous moles (melanomas) often exhibit blurred or jagged edges.
  • Color: When a mole has different color shades, this needs to be evaluated by a doctor, as normal moles usually have only one color.
  • Diameter: Every mole, regardless how normal it might look otherwise, that is larger than a quarter inch, should be checked by a dermatologist, as well as moles that suddenly started expanding.
  • Evolving: Any mole that exhibits a change (in size, color, symmetry, borders, but also itching, flaking, and so on) should be examined by a professional.

If you notice any of these things, or are worried for another reason, act safe and consult a physician.

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Figure 1: Illustration of the ABCDE rule.

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