Most moles are harmless, but certain visual features can signal that a mole has become cancerous or is heading that way. The key is knowing what to look for: irregular shapes, uneven colors, changes over time, and moles that simply look different from all your others. When melanoma is caught early and still confined to the skin, the five-year survival rate is about 98%. When it’s caught late and has spread to distant organs, that number drops to roughly 16%. Learning to spot the warning signs genuinely saves lives.
The ABCDE Rule
The most widely used framework for evaluating a mole is the ABCDE rule, developed to describe features of early melanoma. Each letter flags a specific trait worth examining.
Asymmetry: Draw an imaginary line through the middle of the mole. If one half doesn’t match the other in shape, that’s asymmetry. Normal moles tend to be roughly round or oval and fairly symmetrical.
Border: Look at the edges. Cancerous moles often have ragged, notched, or blurred borders, and the pigment may seem to bleed into the surrounding skin. Healthy moles usually have smooth, well-defined edges.
Color: A single mole shouldn’t contain a patchwork of colors. Melanomas often show shades of brown, tan, and black mixed together, sometimes with areas of white, gray, red, pink, or blue. A mole that’s one uniform shade of brown is far less concerning than one with multiple colors swirled together.
Diameter: Most melanomas are larger than 6 millimeters across, roughly the size of a pencil eraser. That said, melanomas can be tiny, so size alone doesn’t rule anything out. A mole that’s growing is more important to watch than one that’s simply large.
Evolving: This is arguably the most important letter. Any mole that has changed in size, shape, color, or texture over weeks or months deserves attention. New symptoms like itching, bleeding, or crusting also fall under “evolving.”
The Ugly Duckling Sign
Sometimes the most useful screening tool is comparison. The “ugly duckling sign” refers to a mole that simply looks different from all the others on your body. Most people’s moles share a family resemblance: similar size, color, and shape. If one mole stands out as the odd one, that outlier deserves a closer look, even if it doesn’t clearly meet every ABCDE criterion. Your eye is often picking up on subtle irregularities before you can articulate exactly what’s wrong.
Raised, Firm, and Fast-Growing Moles
The ABCDE rule works well for the most common forms of melanoma, but one aggressive type doesn’t always play by those rules. Nodular melanoma tends to grow upward off the skin rather than spreading outward, so it may not look like a typical flat, irregularly shaped mole. Instead, it appears as a firm, dome-shaped bump that’s often dark brown, black, or sometimes reddish or skin-colored. It feels hard to the touch, not soft or squishy like a benign skin tag.
The hallmark of nodular melanoma is speed. It can grow noticeably over just a few weeks. Dermatologists sometimes use the “EFG” rule for this type: Elevated, Firm, and Growing. If you notice a new raised bump that’s firm and getting bigger quickly, don’t wait to have it checked.
Melanoma on Palms, Soles, and Nails
There’s a common misconception that melanoma only appears on sun-exposed skin. Acral lentiginous melanoma develops on the palms of the hands, soles of the feet, or under fingernails and toenails. It’s the most common type of melanoma in people with darker skin tones, and it’s frequently diagnosed late because people mistake it for a bruise, blood blister, or wart.
On the palm or sole, it usually appears as an unevenly pigmented brown or black spot that looks different from the surrounding skin and grows over time. Under a nail, it may show up as a dark streak or pigmented band running from the cuticle to the tip. The CUBED mnemonic helps identify these: look for unusual Color, an Uncertain diagnosis (something you can’t explain), Bleeding, Enlargement, and Delay in healing. If a “bruise” on your foot hasn’t healed in a few weeks, or a dark line under your nail is widening, those are red flags.
What Looks Cancerous but Isn’t
Not every alarming-looking spot is melanoma. Seborrheic keratoses are among the most common benign growths, and they can look surprisingly scary. They’re waxy, raised, brown or black spots that sometimes appear suddenly. They can even have a bluish sheen that mimics a feature seen in melanoma. The key difference: seborrheic keratoses tend to have a “stuck-on” appearance, as if you could peel them off, and often contain tiny white cysts or dark pore-like openings visible on their surface. Melanomas lack these features and are more likely to show structural irregularity and multiple distinct patterns when examined closely.
Other benign look-alikes include cherry angiomas (small, bright red bumps), dermatofibromas (firm brownish bumps often on the legs), and dysplastic nevi (atypical moles that are larger and more irregular than normal moles but still benign). Having atypical moles doesn’t mean you have cancer, but it does mean you should monitor them more carefully.
How to Do a Skin Self-Exam
The American Academy of Dermatology recommends a systematic head-to-toe approach. You’ll need a full-length mirror, a hand mirror, and good lighting. The whole process takes about 10 minutes once you’re familiar with it.
- Front and back: Stand in front of a full-length mirror and examine your entire body front and back, then raise your arms and check both sides.
- Arms and hands: Bend your elbows and carefully examine your forearms, underarms, fingernails, and palms.
- Legs and feet: Check the backs of your legs, the spaces between your toes, your toenails, and the soles of your feet.
- Neck and scalp: Use a hand mirror to examine the back of your neck, then part your hair section by section to look at your scalp.
- Back and buttocks: Use a hand mirror (or ask a partner) to check your back and buttocks.
The goal isn’t to diagnose anything yourself. It’s to establish a baseline so you notice when something changes. Taking photos of moles you want to track can make month-to-month comparison much easier.
What Happens at the Dermatologist
When you bring a suspicious mole to a dermatologist, the first step is usually dermoscopy: a handheld magnifying device with a light that lets the doctor see structures beneath the skin’s surface invisible to the naked eye. They’re looking for patterns in how pigment is distributed, whether the architecture of the mole is orderly or chaotic, and whether specific features associated with malignancy are present, like irregular blood vessel patterns, off-center pigment clusters, or blue-gray coloring deep in the skin.
If a mole looks suspicious under dermoscopy, the next step is a biopsy. The preferred approach is usually to remove the entire growth when possible. An excisional biopsy removes the whole mole plus a small margin of healthy skin around it, using a scalpel, and typically requires a few stitches. A punch biopsy uses a small circular blade to remove a deeper core of tissue and may also need stitches depending on the size. The removed tissue goes to a lab, and results usually come back within one to two weeks.
A biopsy is the only way to confirm whether a mole is cancerous. No visual assessment, no matter how expert, can provide a definitive diagnosis without examining the cells under a microscope. If the biopsy comes back positive for melanoma, the pathology report will include details about how deep the cancer has grown, which determines the next steps for treatment.