A cancerous mole typically looks different from your other moles in specific, recognizable ways: it’s asymmetrical, has irregular borders, contains multiple colors, measures larger than 6 millimeters (about the size of a pencil eraser), or has visibly changed over recent weeks or months. These five features, known as the ABCDE criteria, are the standard framework dermatologists use to flag suspicious spots. But not all skin cancers look like dark, irregular moles. Some are pink, pearly, or even skin-colored, which makes knowing the full range of warning signs important.
The ABCDE Signs of Melanoma
Melanoma is the most dangerous form of skin cancer, and catching it early dramatically improves outcomes. The ABCDE rule, developed by the National Cancer Institute, breaks down the visual red flags into five categories:
- Asymmetry: If you drew a line through the middle of the mole, the two halves wouldn’t match. Normal moles tend to be roughly symmetrical.
- Border: The edges are ragged, notched, or blurred rather than smooth. The pigment may visibly spread into the surrounding skin.
- Color: Instead of one uniform shade, the mole contains a mix of brown, tan, and black. You may also see patches of white, gray, red, pink, or blue within the same spot.
- Diameter: Most melanomas are larger than 6 millimeters wide, roughly the diameter of a pencil eraser. That said, melanomas can be smaller. Lesions larger than 6 mm are significantly more likely to be melanoma on biopsy, but the 6 mm threshold isn’t a guarantee of safety below it.
- Evolving: The mole has changed in size, shape, or color over the past few weeks or months. New symptoms like itching, burning, or bleeding also count as evolution.
A mole doesn’t need to check every box to be suspicious. Even one of these features, particularly a mole that’s actively changing, warrants a closer look.
The “Ugly Duckling” Rule
Beyond the ABCDE criteria, there’s a simpler visual test. Most people’s moles share a family resemblance: they’re roughly the same color, size, and shape. The “ugly duckling sign” refers to any mole that stands out from its neighbors. If one spot on your arm looks noticeably different from all the others around it, that outlier deserves attention, even if it doesn’t clearly meet the ABCDE criteria.
Melanomas That Don’t Look Dark
About 5 percent of melanomas are amelanotic, meaning they lack the dark pigment most people associate with skin cancer. These appear as pink, red, or skin-colored bumps or patches. Because they don’t match the typical image of a dangerous mole, amelanotic melanomas are often overlooked or mistaken for harmless irritations, which means they tend to be diagnosed at a later stage compared to darker melanomas.
Any subtype of melanoma can appear this way. If you have a new pink or reddish bump that isn’t healing, doesn’t match a typical pimple or bug bite, or is slowly growing, it’s worth having it checked.
Skin Cancer on Palms, Soles, and Under Nails
A form called acral lentiginous melanoma develops only on the palms of the hands, soles of the feet, or under the fingernails and toenails. Unlike most melanomas, which occur more often in people with lighter skin, this type occurs at similar rates across all skin tones. It often appears as a dark streak under a nail, or a darkening patch on the palm or sole.
People with darker skin are less likely to know someone who’s had skin cancer, and less likely to think about checking these areas. But these hidden locations are exactly where melanoma is most likely to develop in people of color, making self-checks of the hands, feet, and nail beds especially important.
Other Skin Cancers That Aren’t Moles
Not all skin cancer starts in a mole. Basal cell carcinoma and squamous cell carcinoma are more common than melanoma, and they look quite different.
Basal Cell Carcinoma
This typically appears as a shiny, translucent bump. On lighter skin, it looks pearly white or pink. On darker skin, it often appears brown or glossy black. You may notice tiny blood vessels on the surface. These bumps can bleed, scab over, and then seem to heal before reopening. They grow slowly and rarely spread to other parts of the body, but they can cause significant local damage if ignored.
Squamous Cell Carcinoma
This one is more varied in appearance. It can show up as a firm bump that may be skin-colored, pink, red, brown, or black. It can also look like a flat sore with a scaly crust, a rough patch on the lip, or a new raised area on an old scar. Wart-like sores are another presentation. Unlike basal cell carcinoma, squamous cell carcinoma can spread if left untreated.
Spots That Look Suspicious but Aren’t
Seborrheic keratoses are one of the most common benign growths that get mistaken for skin cancer. They’re waxy, flat or slightly raised, painless, and often look like unusual scabs stuck onto the surface of the skin. That “stuck-on” quality is their hallmark. They can be dark brown or black, which sometimes triggers alarm, but their waxy texture and well-defined edges set them apart from melanoma. Still, if you can’t tell the difference by sight alone, a dermatologist can confirm it quickly.
What a Dermatologist Does With a Suspicious Spot
When you bring a concerning mole to a dermatologist, the first step is usually examination with a dermatoscope, a handheld magnifying tool with built-in lighting. Under magnification, the dermatologist looks for structural patterns invisible to the naked eye: irregular pigment networks with uneven lines and holes, blue-white structures, and asymmetry in both color and architecture. If any two of these three features are present, the lesion typically gets biopsied.
A biopsy involves removing all or part of the spot, usually under local anesthesia, and sending it to a lab. The procedure itself takes minutes, and results generally come back within one to two weeks. If the spot turns out to be benign, no further treatment is needed. If it’s melanoma, the stage and depth determine what happens next.
How to Check Your Own Skin
A monthly self-exam is the most practical way to catch changes early. Stand in front of a full-length mirror and use a hand mirror for your back, scalp, and the backs of your legs. Check between your toes, the soles of your feet, your palms, and your nail beds. You’re not looking for a specific diagnosis. You’re looking for anything new, anything different, and anything that’s changed.
Pay particular attention to moles that have shifted in color, grown in size, developed an irregular border, or started itching or bleeding. Photograph spots you want to track so you have a visual reference point next month. The goal isn’t to become your own dermatologist. It’s to notice changes early enough that treatment stays simple.