How to Tell If a Mole Is Turning Into Skin Cancer

Changes in Appearance Can Be the Sign of Melanoma

Health experts recommend that we check our skin every month for signs of skin cancer and melanoma, but how do we really know whether a mole or freckle is normal or abnormal? And what if you have a lot of moles on your body, including hard-to-see spots on your back or neck? Where do you even start?

While a dermatologist is the only person who can truly differentiate between a normal and abnormal mole, there are a few things you can do at home to preemptively spot a troublesome blemish. 

Start by understanding that melanoma, while more common in fair-skinned people, can happen to anyone, and not just those who have had excessive sun exposure. Genetics and family history play a huge part in determining whether a person may or may not get cancer so it's always best to avoid making assumptions about your own personal risk. 


The ABCDE Rule of Melanoma

Self-examination can sometimes be tricky, but there a few simple tips that can help. Start by knowing the ABCDE Rule of skin cancer and melanoma.

The ABCDE Rule

The ABCDE Rule is a tool to help you identify abnormalities when examining moles, freckles, and other skin blemishes on your body. Each letter represents an abnormal characteristic: asymmetry, border, color, diameter, and evolution.

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Melanoma in situ
Melanoma in situ.  DermNet / CC BY-NC-ND

These are just general signs to watch for as not all developing skin cancers have these traits. Some might have discoloration but still be symmetrical. Other may be growing quickly but have no other characteristics on the list.

The ABCDE Rule is pretty simple to remember:

  • Asymmetry - Normal moles or freckles are completely symmetrical. If you were to draw a line through one, you would have two symmetrical halves. In some skin cancers, spots will not look the same on both sides. 
  • Border - The borders or edges of a melanoma are often irregular, jagged or blurry.
  • Color - Normal moles are uniform in color. Moles are considered abnormal when they have more than one color or different shades. This can include the lightening or darkening of a mole. The "classic" appearance of a melanoma is often referred to as being "red, white, and blue" in color. 
  • Diameter - If a mole is larger than a pencil eraser (about 1/4 inch or 5 mm), it is considered to be abnormal. This includes moles that do not have any other notable abnormalities.
  • Evolution and/or Elevation - Evolution refers to any changes in the symmetry, borders, colors, or diameter of an existing mole. Elevation refers to a mole which is elevated or has variations in height.

While typically not a part of the ABCDE Rule, some healthcare providers have begun to add the letter "F" for "funny-looking." It simply suggests that gut reaction plays a part if determining whether a blemish may or may not be of concern. If you consider a mole or freckle funny-looking — whether it be excessively dry, itchy, or just "off" — get it checked out today.

A Word From Verywell

If you encounter an abnormal mole or freckle anywhere on your body, try not panic. Simply make your earliest appointment to see your healtcare provider or, more preferably, a licensed dermatologist. It may turn out to be nothing, but, even if it is, you're at least in the position to get it treated early.

And remember that sun exposure is not the only cause for sudden skin abnormalities. Hormonal changes during puberty and pregnancy can also cause skin changes, usually harmless. 

Meanwhile, if you have a lot of freckles and moles, keep a digital photo catalog of them. Ask a friend or family member to help if they're on your back or someplace else that's hard to monitor. You can then make monthly comparisons to see if there are any changes and compare them to our gallery of normal and abnormal moles as a reference point.

And, finally, if after an examination your healthcare provider tells you there's nothing to worry about but you're still concerned, don't hesitate to get a second opinion. There is no such thing as being too cautious when it comes to melanoma.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Skin Cancer Foundation. Self-exams save lives.

  2. Skin Cancer Foundation. Melanoma risk factors.

  3. National Cancer Institute. Common moles, dysplastic nevi, and risk of melanoma.

Additional Reading
  • Markovik, S.; Erickson, S.; Rao, R.; et al. "Malignant Melanoma in the 21st Century, Part 1: Epidemiology, Risk Factors, Screening, Prevention, and Diagnosis." Mayo Clinic Proceedings. 82(30):364-380.

By Lisa Fayed
Lisa Fayed is a freelance medical writer, cancer educator and patient advocate.