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. The rules describe the physical condition and/or progression of any skin abnormality, which helps in determining whether it has features of cancer.


Watch Now: The ABCDE Rule of Melanoma

The Basics About Skin Cancer

By definition, skin cancer is the abnormal growth of skin cells. Some types of skin cancer can invade deeper layers of the skin or may spread and damage other areas of the body.

  • 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, especially for 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 how quickly it develops.

Types of Skin Cancer

The major types of skin cancer are categorized by the type of cells they directly affect. Skin cancer typically begins in the top layer of skin called the epidermis, which provides a protective layer of cells that your body continually sheds.

The epidermis contains three main types of cells:

  • Squamous cells lie just below the outer surface.
  • Basal cells lie beneath the squamous layer and produce new skin cells.
  • Melanocytes 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 prognosis (likely outcome). The appearance of the skin may provide a clue as to which type of cell is involved, but a skin biopsy is needed for a definitive diagnosis.

The ABCDE Rule of Skin Cancer

Checking your own skin for changes can help identify melanoma in its earliest stages. This can increase your chance of 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. The shape alone doesn’t suggest a malignancy, since some birthmarks are irregular in shape, but is 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 cancerous or pre-cancerous growth.

C for Color

  • Normal moles and spots are usually one color.
  • A mole that has more than one color should be considered suspicious. Color changes can include the darkening of a spot (sometimes to dark purple or black) or lightening in certain parts of the growth.

D for Diameter

  • If a skin 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 Evolution

  • Typically, birthmarks do not change significantly.
  • Evolution means that the mole or growth is changing in size, appearance, and texture, or causing new symptoms (such as itching, pain, or bleeding).


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, 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 (even cost) of a healthcare provider’s visit. Make your appointment today.

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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. Ward, W., Lambreton, F., Goel, N., Yu, J. and Farma, J. (2017). Clinical presentation and staging of melanomaCutaneous Melanoma: Etiology and Therapy, pp.79-89. doi:10.15586/codon.cutaneousmelanoma.2017.ch6

  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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