Cancerous Moles: Melanoma Symptoms and Causes

Not all atypical moles turn into melanoma, and not all melanomas develop from an atypical mole.

Moles are common skin growths that tend to pop up throughout our lives. Most people have around 10 to 40 moles. They signal our uniqueness, often appearing flat or raised; brown, pink, black, or blue; and smooth or wrinkly.

For the most part, moles are common and harmless. But sometimes, they can become cancerous due to excessive ultraviolet (UV) exposure from sunlight or tanning beds. Namely, melanoma can develop when a mole's appearance—including the shape, color, and size—changes drastically or a new mole appears.

Melanoma occurs in the cells that typically produce your skin pigmentation, called melanocytes. It is uncommon compared to other skin cancers—like basal and squamous cell—only accounting for about 1% of all cases. However, melanoma is the deadliest type of skin cancer, according to the American Cancer Society (ACS).

Here's everything you need to know about skin cancer symptoms, causes, and treatments.

Dermatologist performing skin cancer screening and examining moles on patient
Pixel-Shot / Adobe Stock

What Is a Cancerous Mole?

A mole, technically known as a melanocytic nevus, is a common skin growth that develops during childhood or later in life. Moles appear when skin pigmentation cells grow in clusters, creating an overgrowth, per the National Cancer Institute (NCI).

Common moles are usually small, have a round and smooth surface, and are dome-shaped, according to the NCI. They are also typically pink or brown, the color generally coordinating with your complexion tone. That means that people with fairer skin tones and lighter hair colors may have lighter moles, while people with darker skin tones and hair colors may have darker moles.

"When we talk about moles, there are congenital moles—like birthmarks—moles that are completely benign, and then there are [dysplastic] moles with some atypic, meaning under the microscope we see atypical or odd-looking cells," Mary L. Stevenson, MD, a dermatologic surgeon in New York City, told Health.

A dysplastic nevus, also known as an atypical mole, may be larger than a common mole, per the NCI. Atypical moles can be flat or raised and can have irregularly shaped borders and multiple colors. Because they contain atypical cells, they also have a higher chance of becoming cancerous than common moles.

A cancerous mole can pop up on areas of the skin previously free of moles. They can also appear in the eye, digestive system, or in other areas of the body. Melanoma is the deadliest type of skin cancer because it can invade nearby and distant tissue inside the body—like the lungs, liver, bone, or brain. This is also known as metastasizing.

What Causes Melanoma?

The vast majority of atypical moles with not turn into melanoma. And not every melanoma develops from an atypical mole, said Debra Jaliman, MD, a board-certified dermatologist and assistant clinical professor of dermatology at the Icahn School of Medicine at Mount Sinai in New York City. Researchers are unsure about why some moles turn cancerous while others stay benign. Though, there is a handful of contributing risk factors.

"UV light exposure is the single biggest risk factor for the development of cancerous spots," Joshua Zeichner, MD, associate director of cosmetic and clinical research in dermatology at Mount Sinai Hospital in New York City, told Health. "The UV light causes free radical damage to the skin cells and leads to a transformation into an atypical, unregulated cell."

Per the NCI, having a large number of moles—more than 50 common moles or more than five atypical moles—can also increase your risk of melanoma. Other risk factors include having a family history of skin cancer or melanoma, having a weakened immune system, and being older and male.

Warning Signs

Most importantly, common and atypical moles should maintain the same size, shape, and color. You should take notice when any mole, old or new, begins to change.

There are a few different ways to examine moles to see if they are concerning. The first is called the ABCDE method, said Dr. Zeichner, who described the acronym below:

  • A, or Asymmetry: A mole with one side that does not look like the other
  • B, or Border: A mole with a jagged or irregularly shaped border
  • C, or Color: A mole with multiple colors, like brown, black, white, or blue
  • D, or Diameter: A mole with a diameter greater than 6 millimeters, or the size of a pencil eraser
  • E, or Evolution: A mole that changes shape or appearance over time

Other common symptoms of cancerous moles are itchiness, pain, or bleeding at the site of the mole.

You should also keep an eye out for new moles on your skin. Though common, those moles lead to melanoma more often than others. According to the Skin Care Foundation, dermatologists find only 20% to 30% of melanomas in moles existing at birth or during childhood. The other 70% to 80% of melanomas arise in skin previously cleared of moles. So, if you have a new mole that looks concerning, you should consult your healthcare provider.

Diagnosing Atypical Moles and Melanoma

Suppose you or your dermatologist discover a concerning mole. The dermatologist may remove a mole for biopsy. According to Dr. Stevenson, if the biopsy determines that the mole is atypical, the dermatologist will usually place it into one of three categories: mild, moderate, or severely atypical. Depending on your results, the dermatologist may decide to excise the mole entirely.

"Generally speaking, we remove atypical moles that are moderate or severe to ensure [the] entire lesion is out and there was not a sampling error with the biopsy that only took a portion of the specimen," said Dr. Stevenson.

And if a skin biopsy determines melanoma, swift action is necessary because melanoma can spread quickly to other tissues and organs. Depending on the cancer stage and other factors, a team of healthcare providers will devise a plan for treating melanoma.



Per the ACS, surgery is the primary treatment option for melanoma. Surgery is usually able to cure the early stages of cancer. The types of surgery include wide excision, Mohs surgery, lymph node dissection, and metastatic melanoma surgery.

Wide excision removes melanoma and a small area of healthy skin to ensure the removal of all cancerous cells. Mohs surgery involves a dermatologist removing thin layers of skin one section at a time until they detect no cancer cells. Lymph node dissection removes the lymph nodes near melanoma. And if cancer spreads to other tissues inside the body, metastatic melanoma surgery may control melanoma rather than cure it.

In some rare situations, a dermatologist may consider amputation if the melanoma is deep within a digit, like a finger or a toe.


If the melanoma becomes aggressive, a dermatologist may consider other types of therapy. According to the ACS, those therapies include:

  • Immunotherapy: Involves medication to support your immune system and attempts to destroy cancer cells
  • Targeted Therapy: Specifically marks cancer cells and destroys them
  • Chemotherapy: Works by sending medicine intravenously (through the bloodstream)
  • Radiation Therapy: Utilizes high beam rays to get rid of cancer cells

Before considering any of those approaches, you should consult your healthcare provider to determine an appropriate form of treatment.

How Can You Prevent Skin Cancer?

When it comes to protecting yourself from skin cancer, prevention is critical. And while some risk factors—including family history, sex, and age—are beyond your control, there are actions you can take to lower your overall risk.

First, try to limit your UV exposure as much as possible. That means practicing sun safety while outside and wearing sunscreen with an SPF of 30, protective clothing, a hat, and sunglasses. You should also avoid tanning beds, where UV exposure is exceptionally high.

Keeping track of how your skin looks is essential, too. You might visit a dermatologist to receive annual skin checks, per the Skin Cancer Foundation.

Patients who receive a diagnosis of non-melanoma skin cancer should have screening every three to six months for the two years following treatment and then annually thereafter. Patients with melanoma should have screenings every three to six months for the first two years after treatment and then every six months thereafter. If no other skin cancers are identified five years post-surgery, they may also return to annual screenings.

"If you notice a new or changing spot, make sure to get it checked by your dermatologist [as soon as possible]," said Dr. Zeichner. "When detected early, the atypical moles can be removed completely without any risk of progression into skin cancer."


Most moles are common skin growths that differentiate us from others. But sometimes, atypical moles can become cancerous due to excessive UV exposure. Suspicious moles may appear asymmetrical, have jagged borders or multiple colors, or grow bigger than the size of a pencil eraser. A dermatologist can evaluate those moles for melanoma or other skin cancers and determine treatment.

But the best way to avoid skin cancer is through prevention. Practice sun safety, avoid tanning beds, and frequently check your skin for changes.

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