How Can You Tell If It's a Mole or Skin Cancer?

Telling moles and melanoma apart is not always easy, even for dermatologists with years of training and experience. With that said, there are telltale signs that can help differentiate a benign (non-cancerous) skin lesion from a potentially dangerous skin cancer.

The clues are sometimes subtle but may be enough to get you evaluated and diagnosed when the cancer is still treatable.

This article explains the differences between moles and melanoma and some of the signs and symptoms that warrant an immediate investigation by a dermatologist.

What Is a Mole?

Woman with moles on her neck

Alyssa B. Young / Getty Images

A nevus is the medical term for a mole. A mole is a benign melanocytic tumor, meaning a non-cancerous skin lesion that develops from pigment-producing cells called melanocytes.

Also known as beauty marks, moles are not usually present at birth but begin to appear during childhood and the teen years. They can either develop on the skin (in the layer known as the epidermis) or under the skin (in the layer called the dermis).

Most moles never cause any problems, but a person who has more than 50 of them has a higher risk of developing melanoma, the most aggressive form of skin cancer.

Recap

A mole (nevus) is a non-cancerous skin tumor that develops from pigment-producing cells called melanocytes.

What Is Melanoma?

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

Lentigo maligna melanoma

DermNet / CC BY-NC-ND

Melanoma is a type of skin cancer that also develops from pigment-producing melanocytes. The primary cause of melanoma is overexposure to ultraviolet (UV) light from the sun or things like tanning beds.

Early signs of melanoma are changes in the size or appearance of a mole. At later stages, the lesion may get crusty, form ulcers, or bleed. Melanoma usually does not cause pain.

Melanoma is the most dangerous type of skin cancer, affecting more than 230,000 people globally and causing over 50,000 deaths each year. In the United States, males are around 1.5 times more likely to get melanoma than females.

When identified early, melanoma is highly treatable. When it spreads (metastasizes), the five-year survival rate is around 30%. This means that three out of 10 people will survive for at least five years.

Recap

Melanoma is the most dangerous form of skin cancer. It arises from pigment-producing cells called melanocytes. Overexposure to UV radiation from the sun or tanning beds is the primary cause.

The ABCDE Rule of Melanoma

Melanoma Skin Cancer

National Cancer Institute

When checking for early signs of melanoma, it's helpful to use the ABCDE rule. The ABCDE abbreviation stands for:

  • Asymmetry: An irregular shape
  • Border: Ragged, notched, or blurred edges
  • Color: Different colors or shades within the mole
  • Diameter: Diameters over 6 millimeters (though melanoma can come in any size)
  • Evolving: Changes in size, shape, color, or appearance

Recap

Dermatologists use a system called the ABCDE Rule to spot the signs of melanoma based on a lesion's shape, border, color, size, and changes over time.

Moles: Symmetry

normal mole
National Cancer Institute

This is an example of a normal mole. Note that it is almost perfectly round. Melanoma differs in that the lesions are usually asymmetrical (lopsided).

Although most moles are benign, certain types carry a higher risk of developing melanoma. Between 2% and 8% of the White population in the United States have moles that are dysplastic.

Dysplastic moles are not cancer but can become cancerous over time. Unlike normal moles, dysplastic moles are larger than 6 millimeters, irregular in shape, and tend to have uneven coloration, with dark brown centers and lighter, uneven edges.

People with dysplastic moles and a ​family history of melanoma are at high risk of developing melanoma before the age of 40.

Recap

Moles are symmetrical rather than lopsided. However, some moles can become dysplastic—changing in size, shape, and color—and eventually turn cancerous.

Melanoma: Asymmetry

Melanoma skin cancer lesion

Callista Images / Getty Images

This image shows how melanoma tumors are often irregularly shaped (asymmetrical) with uneven coloration. This is not always easy to tell, particularly in the early stages, but there are some tricks you can use.

One is to draw a line through the center of the lesion and see if the two sides match. If they don't and the colors also appear uneven, see a dermatologist.

Also, look at the borders. Are they starting to fade and dissolve into the surrounding skin? This is another telltale sign. Any noticeable change to a mole is worth getting checked out.

Moles: Even Coloration

normal moles
National Cancer Institute

Moles can come in different colors. Some may be pink or flesh-colored, while others may be tan or brown. Some can be small and freckle-like, while others may look like a Cindy Crawford-style beauty mark.

No matter which color, the one feature that characterizes moles is that the color is consistent. You won't see two or three different colors in a mole, but you may with melanoma.

It is worth noting that moles can change in color without becoming cancerous. For example, moles on the face will often start out brown and get lighter over time. Moles can also raise or flatten (though will typically remain the same size).

Recap

Although moles can differ in color, they are recognized by their even coloration.

Melanoma: Uneven Coloration

Close-Up of Malignant Melanoma

DR P. MARAZZI/SCIENCE PHOTO LIBRARY / Getty Images

In addition to asymmetry, uneven coloration is a hallmark of melanoma. The same lesion can have a range of colors, from tan, orange, and brown all the way to red, black, and blue.

Another clue that a person has melanoma is the so-called "ugly duckling sign."

By and large, the moles on people's bodies will all look the same. However, if you step back and look at them in their entirety, there may be some that stand out as being different, either in terms of color, size, or shape. These "ugly ducklings" may be an early sign of melanoma.

Recap

Melanoma is often recognized by its uneven coloration. Another clue is the "ugly duckling sign" in which a mole may stand out from all of the others on a person's body.

Moles: Defined Borders

normal mole
National Cancer Institute

Normal moles generally have well-defined borders along with uniform coloration. They can be raised or flat. Some moles may be bigger than others, but most are around 1 to 2 millimeters in diameter.

Despite these differences, the vast majority of moles have smooth borders that are clearly separated from the surrounding skin. The color of the mole will also be even rather than mottled.

Melanoma: Irregular Borders

Melanoma Skin Cancer

National Cancer Institute

Notice how this melanoma tumor has a border that is uneven, ragged, and notched. The color also appears to "bleed" around the edges.

An uneven border is one of the telltale signs of melanoma. By contrast, moles tend to have smoother, more even borders.

It is worth noting that around 20% to 30% of melanomas develop from existing moles, while 70% to 80% arise on seemingly normal skin. In either case, melanoma tumors will commonly have jagged, uneven borders that set them apart from other benign skin conditions.

Recap

A mole with an uneven, jagged, or notched border is another telltale sign of melanoma. The cancer may arise in an existing mole or appear spontaneously out of nowhere.

Melanoma: Changes of Any Sort

Melanoma Skin Cancer

Skin Cancer Foundation

The final photograph is of a melanoma tumor that is large and had gotten bigger over time. Any change in the size, shape, color, or appearance of a mole is an immediate red flag that melanoma may be involved.

The challenge, of course, is recognizing the changes. Unless you do a regular self-examination, you may not even notice a mole has changed unless it is bleeding or has caused a skin ulcer. This is especially true if you have lots of moles.

Another challenge is monitoring changes on parts of the body you can't easily examine, such as the back. A friend or mirror can certainly help, but a better option may be to have a regular, full-body check-up with a dermatologist.

The Skin Cancer Foundation is among the organizations that endorse once-yearly skin exams.

Recap

As a rule, any change to the size, shape, color, or appearance of a mole warrants an investigation by a dermatologist. Many health authorities endorse yearly full-body checkups to spot skin cancer early.

Skin Cancer Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Man

Summary

Moles and melanoma can be hard to tell apart, but doctors use a system called the ABCDE rule to help spot lesions that may be cancerous.

The ABCDE rule is based on the fact that melanoma tumors tend to be asymmetrical, have ill-defined borders, be unevenly colored, be larger than 6 millimeters in diameter, and change over time. These early signs can help spot melanoma early when it is still highly treatable.

In addition to doing regular self-exams at home, an annual, full-body checkup with a dermatologist is often recommended.

Frequently Asked Questions

  • What causes moles to suddenly appear?

    Aging is one reason for moles to suddenly appear. In most cases, it is normal to see new moles appear on the body until you are 40 years old. When a mole shows irregular changes in size, shape, or color, it should be reported to a healthcare provider in case the mole turns out to be melanoma.

  • Why do moles form?

    Moles form due to an increased growth of melanocytes, a type of skin cell. This growth usually takes place during childhood, but it is possible for moles to appear at birth or shortly after. Body parts regularly exposed to ultraviolet radiation created by the sun are more likely to develop moles, but genetic factors may be responsible for mole growth as well.

  • How does a mole get infected?

    A mole can get infected from outside bacteria or debris that finds its way inside. One way this may happen is from shaving; if a razor cuts open the top and exposes the inside, outside bacteria can cause an infection. If this happens, a healthcare provider may need to see the mole and remove it.

  • What do abnormal moles look like?

    Abnormal or atypical moles are often larger than a dime, asymmetrical or not round in shape, and appear as a mixture of colors including red, pink, tan, and brown. Atypical moles are known as dysplastic nevus. Some dysplastic nevus can resemble melanoma, even if they are not cancerous. However, the risk of getting melanoma increases when you have at least four atypical moles.

12 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.
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By Timothy DiChiara, PhD
Timothy J. DiChiara, PhD, is a former research scientist and published writer specializing in oncology.