The ABCDE skin cancer rule is a way to help people spot the potential signs of melanoma. It stands for asymmetry, border, color, diameter, and evolving.

According to the American Cancer Society, cancer of the skin is the most common cancer, with melanoma accounting for the majority of skin cancer deaths. Spotting signs early is important for successful treatment and a positive outcome.

This article briefly explains what skin cancer is before looking at each ABCDE category. It also highlights other signs and symptoms of skin cancer and when it might be a good idea to talk with a doctor.

According to the American Academy of Dermatology, signs that a new mole or mark may be melanoma are:

Learn more about melanoma here.

Cancer happens when cells start to multiply uncontrollably, forming tumors. Cancer can develop anywhere in the body, including the skin.

There are three main types of skin cancer:

  • Squamous cell cancer: This is cancer that develops in the flat cells on the epidermis, which is the upper layer of the skin.
  • Basal cell carcinoma: This is cancer that develops in the round cells underneath the squamous cells.
  • Melanoma: This is cancer that starts in the melanocytes, which are in the lower part of the epidermis and make the skin pigment melanin.

If doctors do not diagnose melanoma early, it can spread to other parts of the body.

Learn more about skin cancer here.

According to the American Cancer Society, the most important early signs of melanoma are:

  • a new mark on the skin
  • a mark that changes in size, shape, or color

Other signs include:

  • a mark that looks different from others on the skin, sometimes called the “ugly duckling” sign
  • a sore that does not heal
  • the pigment of the mark spreads outside of its border and into the surrounding skin
  • redness or swelling outside of the border
  • changes in sensation on and around the mark, which may feel itchy, tender, or painful
  • changes in the surface of the mark, which may look scaly or lumpy, or ooze or bleed

Learn more about the symptoms of skin cancer.

Anyone who spots any potential signs of skin cancer should talk with a doctor. The earlier a doctor diagnoses melanoma, the easier it is for them to treat it.

The American Academy of Dermatology offers the following steps to check for signs of skin cancer:

  1. Using a full-length mirror, examine the front and back of the body, then the left and right side, with arms raised.
  2. Look at the palms of the hands, forearms, and underarms.
  3. Look at the soles of the feet, between the toes, and the legs.
  4. Using a hand mirror, look at the neck and scalp.
  5. Using a hand mirror, check the back and the buttocks.

The right treatment depends on the person and whether their cancer has spread.

Doctors may recommend one of the following treatments or a combination of them:

  • surgery
  • immunotherapy
  • chemotherapy
  • radiation therapy

Doctors may talk about a person’s outlook in terms of 5-year survival rates. These statistics refer to the percentage of people with cancer who are expected to be alive 5 years after their diagnosis.

The rates differ according to the stage, or severity, of cancer. Doctors typically define skin cancers as:

  • localized, meaning cancer has not spread
  • regional, meaning cancer has spread to nearby parts of the body
  • distant, meaning cancer has spread to distant parts of the body

Each of these stages has a different 5-year survival rate. According to the American Cancer Society, the 5-year relative survival rates for melanoma are as follows:

  • Localized: More than 99%, meaning out of every 100 people with localized melanoma, more than 99 will still be alive 5 years later.
  • Regional: 71%, meaning out of every 100 people with regional melanoma, 71 will still be alive 5 years later.
  • Distant: 32%, meaning out of every 100 people with distant melanoma, 32 will still be alive 5 years later.

These figures are just a guide and cannot predict one person’s outcome. Each case of melanoma is different. A doctor can better predict a person’s outcome based on individualized factors.

Too much exposure to ultraviolet (UV) rays causes most skin cancers. UV rays from the sun, tanning beds, and sunlamps can all damage skin cells.

People can help prevent skin cancer. The Centers for Disease Control and Prevention (CDC) recommends people:

  • stay in the shade 10 a.m.–4 p.m., when UV rays are at their strongest
  • cover the arms and legs
  • wear a hat that shades the face, head, ears, and neck
  • wear sunglasses that block UV rays
  • use sunscreen with a minimum sun protection factor (SPF) of 15
  • not use tanning beds or sunlamps

Experts developed the ABCDE skin cancer rule to help people spot the signs of melanoma.

The ABCDE rule describes five characteristics that could mean a new mark on the skin is cancer. Anyone who spots any of the signs should talk with a doctor. The earlier doctors can diagnose melanoma, the easier it will be for them to treat it.

People can help prevent skin cancer by limiting sun exposure and avoiding indoor tanning.