Skin Cancer Home > The ABCDE Signs of Skin Cancer: "D" Is for Diameter

Big Moles, Little Moles

Moles usually start to develop while we are young and peak around age 20 to 30. Most people will have at least 25 moles on their body. Once a month, you should make it part of your routine to check these moles -- every one of them! By using mirrors or having someone help you check the ones you can't see (like on your scalp), you should get a good idea of where your moles are located and what they look like. This will make it easy for you to identify a new spot or to notice if a mole you already had is starting to change in shape, size, or color.
However, having moles doesn't necessarily mean you will have skin cancer. Moles are formed when certain skin cells that make the brown pigment (called melanocytes) form growths. The noncancerous growths are called moles, while the cancerous ones are called melanomas.
Melanomas develop when the DNA in the skin cells becomes damaged, such as by UV radiation. This triggers mutations that cause the skin cells to multiply rapidly and form malignant tumors. These tumors originate in the melanocytes in the skin. Melanomas can be new spots or they may develop in moles that were originally "normal."
It is important to know the differences between moles that are normal and those that may be melanomas. The diameter of the mole is one of the ways that can help you distinguish between the two.
Melanomas tend to be larger in diameter than the size of the eraser on a pencil (¼ inch or 6 millimeters). Normal moles are usually not this big. Although melanomas can be smaller than this when they are first detected, in a majority of cases, they are usually larger than 6 millimeters when they are identified.
Also, if you notice that one of your moles is getting bigger, it is a good idea to let your dermatologist or healthcare provider know. If melanoma is caught early, it is often curable. So if new spots develop or if your previous moles are becoming larger, it's time to get them checked out.
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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