Answer:
The ABCDE Rule is broken down as follows:
A for Asymmetry - Normal moles or freckles are typically symmetrical. If you were to draw a line through the center, you would have two symmetrical halves. In cases of skin cancer, spots will not look the same on both sides. (Shape alone doesn’t suggest a malignancy, since some birthmarks will irregular in shape, but is certainly one of the features healthcare providers look for when identifying skin cancers.)
B for Border - Moles, spots, or “beauty marks" are typically round and of no cause for concern. Those with a blurry and/or jagged edge can be a sign of a cancerous or pre-cancerous growth.
C for Color - A mole that has more than one color should be considered suspicious. Normal moles and spots, by contrast, are usually one color. Color changes can include the darkening of a spot (sometimes to dark purple to black) or a lightening in certain parts of the growth.
D for Diameter - If a growth is larger than a pencil eraser (about 1/4 inch or 6mm), it needs to be checked by a healthcare provider. This includes areas of skin that do not have any other abnormalities in terms of color, border, or asymmetry. This is not to suggest that smaller growths don't warrant investigation — including skin tags (acrochordons) — but those over 1/4 inches will always be of particular concern.
E for Elevation - Elevation means that the mole or growth is raised and has an uneven surface. It is both the irregularity of the surface and changes in size that should raise the red flag, particularly if the growth different from any other blemish on the body.