The most reliable way to tell if a mole might be cancerous is to check it against five visual features known as the ABCDE criteria: asymmetry, irregular borders, uneven color, a diameter larger than 6 millimeters (about the size of a pencil eraser), and any evolution or change over time. Catching melanoma early makes an enormous difference. When it’s found while still localized to the skin, the five-year survival rate is 97.6%. When it’s found after spreading to distant parts of the body, that number drops to 16.2%.
The ABCDE Rule for Checking Moles
Dermatologists use this five-point checklist as a first-pass screening tool, and you can use it at home during a self-exam. Each letter points to a specific visual feature of early melanoma.
- Asymmetry: If you drew a line down the middle of the mole, the two halves wouldn’t match. Normal moles tend to be roughly symmetrical.
- Border: The edges look ragged, notched, or blurred rather than smooth and well-defined. The pigment may seem to bleed into the surrounding skin.
- Color: Instead of a single uniform shade of brown, you see a mix of colors. Shades of black, tan, brown, white, gray, red, pink, or blue within a single mole are a warning sign.
- Diameter: Most melanomas are larger than 6 millimeters across, roughly the width of a pencil eraser. That said, melanomas can be smaller than this. A study published in einstein (São Paulo) found that out of 81 patients with lesions 6 mm or smaller, 29 had invasive melanoma. Size alone should never be the reason you dismiss a suspicious spot.
- Evolving: Any change in size, shape, color, or texture over weeks or months is the single most important thing to watch for. A mole that looked fine a year ago but is now growing, darkening, or becoming raised deserves attention.
You don’t need all five features to be concerned. Even one, particularly evolution, is enough reason to have a mole examined.
The Ugly Duckling Sign
The ABCDE criteria evaluate a single mole in isolation, but there’s a complementary approach that works by comparison. The “ugly duckling sign” asks you to look at your moles as a group and identify any mole that looks obviously different from the rest. Most people have a personal pattern: their moles tend to share a similar size, shape, and color. An outlier, whether it’s a single large dark mole surrounded by smaller lighter ones, or a small pale mole in a cluster of darker ones, is the ugly duckling.
This method is especially useful for moles that might not clearly fail the ABCDE test on their own but still look “off” compared to your other spots. If a mole stands out from its neighbors and also shows any ABCDE features, it should be evaluated promptly.
Physical Symptoms Beyond Appearance
Visual changes are the earliest and most common warning, but cancerous moles can also produce physical sensations. New itchiness in a mole that was previously unremarkable, pain or tenderness, bleeding without injury, or crusting and oozing are all signs that something may be changing beneath the surface. A mole that becomes ulcerated, meaning the skin over it breaks down and doesn’t heal, is particularly concerning.
These symptoms often appear later in the progression than visual changes do. If a mole is bleeding or not healing, that generally means it’s been developing for a while, which makes prompt evaluation more urgent.
Moles That Don’t Look Like Melanoma
Not all melanomas follow the textbook appearance. Amelanotic melanoma is a subtype that produces little or no pigment. Instead of the dark, multicolored lesion most people picture, it often looks like a pink or red bump, a flat pinkish patch, or a flesh-colored nodule. It accounts for roughly 2% of melanoma cases but tends to be diagnosed later because it doesn’t trigger the usual alarm bells. By the time it’s found, amelanotic melanoma typically has a greater depth of invasion, higher rates of ulceration, and lower survival rates than pigmented melanoma.
This is why evolution matters more than any single visual feature. A pink bump that’s growing, changing texture, or not healing deserves the same scrutiny as a dark irregular mole.
Spots on Palms, Soles, and Under Nails
Melanoma can also develop in places most people never think to check. Acral lentiginous melanoma appears exclusively on the palms of the hands, the soles of the feet, or under the fingernails and toenails. It’s the most common type of melanoma in people with darker skin tones, though it can affect anyone.
On the palms or soles, it typically starts as an unevenly pigmented black or brown spot that looks different from the surrounding skin and grows over time. Under a nail, it may show up as a dark streak or band of color running from the cuticle to the tip. Patients frequently mistake these spots for bruises, blood blisters, or warts, which delays diagnosis. MD Anderson Cancer Center uses a separate screening acronym for these lesions called CUBED: color that’s unusual, uncertain diagnosis, bleeding, enlargement, and delay in healing.
If you have a dark spot on a palm or sole that you can’t explain with a recent injury, or a streak under a nail that didn’t come from trauma and isn’t going away, get it looked at.
What Looks Cancerous but Isn’t
Seborrheic keratoses are one of the most common benign growths that get mistaken for melanoma. They’re waxy, slightly raised, often darkly pigmented patches that tend to appear after age 40. They can look alarming because of their dark color and rough texture, but a key difference is that they’re usually flat, painless, and have a “stuck on” appearance, as if they were pasted onto the skin’s surface. They also tend to stay stable over time.
Melanoma, by contrast, is more likely to be asymmetrical, multicolored, and actively changing. If you have a dark growth that’s been the same size, shape, and color for years, it’s less likely to be melanoma. But if a spot you assumed was a harmless keratosis starts changing in shape or color, that warrants a second look.
How Dermatologists Evaluate a Suspicious Mole
When you bring a mole to a dermatologist, the first tool they’ll use is a dermatoscope, a handheld magnifying device that makes skin structures appear up to 10 times larger. They’ll apply a small amount of oil or gel to the mole’s surface, then press the lens against your skin. This lets them see pigment patterns, blood vessel structures, and other features beneath the top layer of skin that are invisible to the naked eye.
If the dermatoscope reveals suspicious features, the next step is a biopsy, where part or all of the mole is removed and examined under a microscope. This is the only way to definitively confirm whether a mole is cancerous. The procedure itself is quick, usually done under local anesthesia in the office, and typically takes just a few minutes. Results generally come back within one to two weeks.
How Often to Check Your Skin
A thorough self-exam once a month is a good baseline. Use a full-length mirror and a hand mirror to check your back, scalp, the soles of your feet, and between your toes. Take photos of moles you want to track so you can compare them month to month. Changes are much easier to spot when you have a reference image.
Pay special attention to moles in areas that get regular sun exposure: your face, neck, arms, and upper back. But don’t skip covered areas. Melanoma can develop anywhere on the body, including places that rarely see sunlight.