The ABCDEs of Skin Cancer

An Easy-to-Remember Way to Spot Potential Problems

The ABCDE Rule of skin cancer is an easy-to-remember system for determining whether a mole or growth may be cancerous. They describe the physical condition and/or progression of any skin abnormality that would suggest the development of a malignancy.


Watch Now: The ABCDE Rule of Melanoma

The Basics About Skin Cancer

By definition, skin cancer is the abnormal growth of skin cells. Two types of skin cancer, basal cell carcinoma and squamous cell carcinoma, develop primarily on areas of sun-exposed skin, including the scalp, face, lips, ears, neck, chest, arms, and hands. It is also common on the legs of women.

Melanoma, another type of skin cancer, can develop on parts of the body that rarely see light, including the palms, beneath the fingernails or toenails, and the genital area. The causes for this can vary significantly, as can the speed by which can the cancer develops.

Types of Skin Cancer

In the broad spectrum of skin cancers, three are major types: basal cell carcinoma, squamous cell carcinoma, and melanoma. Each is categorized by the type of cells they directly affect.

Skin cancer typically begins in the top layer of skin called the epidermis. This anatomical structure provides a protective layer of cells that your body continually sheds.

The epidermis contains three main types of cells:

  • squamous cells that lie just below the outer surface
  • basal cells which lie beneath the squamous layer and produce new skin cells
  • melanocytes, which are situated just beneath the basal layer and produce melanin, the pigment which gives skin its color

The type of cell involved helps your healthcare provider determine both the treatment options and the likely outcome (prognosis).

The ABCDE Rule of Skin Cancer

Checking your skin for suspicious changes can help identify melanoma in its earliest stages. This, in turn, can increase your chance for successful treatment.

The ABCDE Rule of skin cancer is not meant to be a tool for diagnosis but rather one by which individuals and healthcare providers can differentiate between a problem growth and a simple, everyday blemish.

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.


The following photo is an example of melanoma that meets most of the ABCDE criteria. However, every case of skin cancer is unique, and a different individual's malignancy could look quite different.

This photo contains content that some people may find graphic or disturbing.

Lentigo maligna melanoma
Lentigo maligna melanoma. DermNet / CC BY-NC-ND

When to See a Healthcare Provider

If you notice any changes to your skin that worry you, don’t hesitate. See your healthcare provider or ask for a referral to a qualified dermatologist. This is particularly true if there is any blemish or growth that changes rapidly or bleeds easily.

While not all skin changes are caused by cancer, the advantages of early diagnosis greatly outweigh the inconvenience (and even cost) of a healthcare provider’s visit. Check it out today.

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Article Sources
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  2. Apalla Z, Nashan D, Weller RB, Castellsagué X. Skin Cancer: Epidemiology, Disease Burden, Pathophysiology, Diagnosis, and Therapeutic ApproachesDermatol Ther (Heidelb). 2017;7(Suppl 1):5–19. doi:10.1007/s13555-016-0165-y

  3. Daniel Jensen J, Elewski BE. The ABCDEF rule: Combining the "ABCDE Rule" and the "Ugly Duckling Sign" in an effort to improve patient self-screening examinationsJ Clin Aesthet Dermatol. 2015;8(2):15.

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