Most moles are harmless, but a cancerous mole typically shows one or more visible warning signs: an uneven shape, irregular borders, multiple colors, a size larger than 6 millimeters (roughly a pencil eraser), or noticeable changes over weeks to months. These five features form the ABCDE framework that dermatologists use, and learning them is the single most useful thing you can do to catch melanoma early.
The ABCDE Framework
Each letter represents a specific visual clue. No single feature confirms cancer on its own, but the more of these a mole has, the more urgently it needs professional evaluation.
- Asymmetry. If you drew a line through the middle of the mole, the two halves wouldn’t match. Normal moles are roughly symmetrical.
- Border. The edges look ragged, notched, or blurred rather than smooth. Pigment may seem to bleed into the surrounding skin.
- Color. Instead of one uniform shade, you see a mix of brown, tan, and black, sometimes with patches of white, gray, red, pink, or blue.
- Diameter. The mole is larger than about 6 millimeters, the size of a pencil eraser. Melanomas can be smaller than this, but most exceed that threshold.
- Evolving. The mole has changed in size, shape, color, or texture over the past few weeks or months. Any new symptom like itching, bleeding, or crusting also counts.
“Evolving” is often the most important letter. A mole that looked fine for years but is now growing, darkening, or developing new colors deserves attention even if it doesn’t check the other boxes.
The Ugly Duckling Sign
Most of your moles share a general family resemblance. They tend to be similar in size, color, and shape. The ugly duckling sign is simple: look for the one mole that doesn’t fit the pattern. It might be darker than all the others, much larger, or just obviously different. That outlier is the one worth having checked, even if it doesn’t clearly meet every ABCDE criterion. This approach is especially helpful for people who have many moles and find it hard to evaluate each one individually.
Skin Cancer Doesn’t Always Look Like a Mole
Melanoma is the type most associated with moles, but the two other common skin cancers have their own appearances.
Basal cell carcinoma often shows up as a shiny or waxy bump that looks translucent or pearly. It can also appear as a flat, scaly patch with raised edges. These lesions may bleed, scab over, and then reopen. They sometimes have a blue, black, or white tint. They grow slowly and rarely spread to other parts of the body, but they can damage surrounding tissue if ignored.
Squamous cell carcinoma tends to look like a firm, skin-colored nodule or a flat, scaly sore that doesn’t heal. It commonly develops on sun-exposed areas like the face, ears, and hands, but can also appear as a rough patch on the lip or inside the mouth.
Melanoma itself can appear as an entirely new growth rather than a change in an existing mole. It’s typically brown or black with an asymmetrical shape, but some melanomas have little to no pigment and appear pink or red.
Hidden Spots Most People Miss
Not all melanomas develop on sun-exposed skin. Acral lentiginous melanoma appears on the palms of the hands, soles of the feet, and under fingernails or toenails. On the hands or feet, it looks like a brown or black discoloration that resembles a bruise or stain but grows over time instead of fading.
Under the nails, this type of melanoma shows up as dark vertical streaks running the length of the nail bed. It’s easy to mistake for dried blood or a fungal infection. As it progresses, the nail may crack or break. This subtype is more common in people with darker skin tones and is frequently diagnosed late because it’s overlooked.
Growths That Mimic Cancer
Seborrheic keratoses are one of the most common benign growths that get mistaken for melanoma. They’re waxy, slightly raised, and often look like they’ve been stuck onto the skin’s surface. Under magnification, dermatologists look for tiny cyst-like structures and pore-like openings within these growths. When those features are present, the likelihood of melanoma drops to essentially zero. But without a trained eye and proper tools, the resemblance can be unsettling, which is a good reason to get anything suspicious evaluated rather than trying to diagnose it yourself.
Who Needs to Be More Vigilant
If you have a large number of moles, especially if some are irregularly shaped or bigger than a third of an inch, you may have atypical mole syndrome. This condition raises your melanoma risk and calls for more frequent monitoring. People with a family history of melanoma in close relatives face an even steeper risk. An inherited condition called familial atypical multiple mole melanoma syndrome makes a person roughly 25 times more likely to develop melanoma.
If you fall into either category, dermatologists typically recommend professional skin exams every three to six months rather than the standard once or twice a year. Monthly self-checks at home become especially important.
How to Do a Monthly Self-Check
Check your skin about once a month, ideally after a bath or shower when your skin is clean and you’re already undressed. You need a well-lit room, a full-length mirror, and a hand mirror.
Start by facing the full-length mirror and examining your entire front, then turn around and check your back. Raise your arms and look at both sides of your body. Bend your elbows and inspect your forearms, upper arms, and palms. Use the hand mirror to see the back of your neck, your scalp (part your hair in sections), and your lower back. Sit down to check the fronts and backs of your legs, between your toes, and the soles of your feet. Don’t skip your nails, the skin between your fingers, and the inside of your mouth, including your lips.
Keep a record of your moles and where they are. A simple phone photo with a date works well. The goal isn’t to diagnose anything yourself. It’s to notice change, because change is the earliest signal you’re likely to catch at home.
What Happens if a Mole Looks Suspicious
A dermatologist will first examine the mole with a dermatoscope, a handheld magnifying device with its own light source. This step dramatically improves accuracy. In a Cochrane analysis, adding dermatoscopy to a visual exam reduced the number of benign lesions falsely flagged as melanoma by roughly 80%, which means fewer unnecessary procedures and more reliable results.
If the mole still looks concerning, the next step is a biopsy. For a suspected melanoma, doctors prefer to remove the entire mole with a small margin of surrounding skin, typically 1 to 3 millimeters. This gives the pathologist the full picture, including how deep the abnormal cells go, which directly affects staging and treatment planning. For very large or awkwardly located lesions where full removal isn’t practical on the first visit, a smaller sample may be taken instead.
The biopsy itself is done under local anesthesia and takes only a few minutes. Results usually come back within one to two weeks. If the mole turns out to be benign or mildly atypical, no further treatment is needed. If melanoma is confirmed, the depth of the cells determines the next steps, which may range from a slightly wider excision to additional testing.