Most moles are harmless, but a mole that looks different from your others or has changed recently deserves a closer look. The key signs to watch for fall into a well-established pattern: asymmetry, irregular borders, multiple colors, a diameter larger than 6 millimeters (about the size of a pencil eraser), and any recent evolution in size, shape, or feel. Catching melanoma early matters enormously. When it’s found before it spreads, the five-year survival rate is effectively 100%.
The ABCDE Rule
Dermatologists use five visual features to flag suspicious moles. You can check these yourself with good lighting and a mirror.
- 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 look ragged, notched, or blurred rather than smooth and well-defined. You might notice pigment that seems to bleed into the surrounding skin.
- Color. Instead of one uniform shade of brown, the mole contains a mix of colors: brown, tan, black, or patches of white, gray, red, pink, or blue.
- Diameter. The mole is larger than 6 millimeters across, roughly the width of a pencil eraser. Melanomas can be smaller than this, but most exceed that threshold by the time they’re noticed.
- Evolving. The mole has changed in the past few weeks or months. Any shift in size, shape, color, or texture counts.
A mole doesn’t need all five features to be suspicious. Even one, especially “evolving,” is reason enough to have it evaluated.
The Ugly Duckling Sign
Sometimes the most useful clue isn’t about a single mole’s features but about how it compares to your other moles. Most people’s moles share a general “family resemblance” in color, size, and shape. A mole that stands out as obviously different from the rest is called an “ugly duckling,” and dermatologists consider this one of the most effective real-world methods for spotting melanoma. If one mole on your back is dark and raised while all the others are flat and light brown, that outlier deserves attention even if it doesn’t clearly match every ABCDE criterion.
Symptoms You Can Feel
Not every warning sign is visual. A mole that starts itching, bleeding, oozing, or crusting without an obvious injury is behaving abnormally. The same goes for a mole that becomes tender or develops a hard, lumpy texture. A sore or spot that doesn’t heal within a few weeks can also signal skin cancer, even if it doesn’t look like a typical mole.
Moles That Don’t Look Like Moles
Some melanomas don’t follow the textbook playbook. Amelanotic melanomas produce little or no pigment, so instead of appearing dark brown or black, they look pink, red, or nearly skin-colored. Because they lack the dark coloring people associate with skin cancer, they’re easy to dismiss as a pimple, scar, or irritation. Any new pink or reddish bump that persists for more than a few weeks, especially one that’s firm or slowly growing, is worth having checked.
Melanoma on Darker Skin Tones
Melanoma is less common in people with darker skin, but it’s often diagnosed at a later, more dangerous stage. One reason is that the most common subtype in people with brown or Black skin, acral lentiginous melanoma, doesn’t appear in the sun-exposed areas most people think to monitor. It shows up on the palms, soles of the feet, and under fingernails or toenails.
On the palms and soles, these lesions often appear as dark brown or black patches with irregular edges. Under a nail, melanoma can look like a dark streak running the length of the nail bed. These spots can also be amelanotic, appearing pink or red instead of dark. The standard ABCDE criteria are less reliable for this subtype. Dermatologists increasingly recommend the “CUBED” rule for acral sites, which flags spots that are colored (any unusual pigmentation), uncertain in diagnosis, bleeding, enlarged, or delayed in healing.
How to Do a Monthly Self-Check
Checking your skin once a month is the simplest way to catch changes early. Do it after a shower in a well-lit room using a full-length mirror and a hand mirror. Start with your front and back, then raise your arms to see both sides of your torso. Bend your elbows and examine your forearms, upper arms, palms, and the spaces between your fingers. Use the hand mirror to check the back of your neck, your scalp (part your hair as you go), and your back.
Don’t skip the places you’d never expect skin cancer: the soles of your feet, between your toes, under your nails, inside your mouth (check your lips, tongue, and inner cheeks), and behind your ears. These hidden spots are exactly where melanoma is most likely to go unnoticed. If you have a partner, ask them to help with hard-to-see areas like your scalp and lower back.
The goal isn’t to diagnose anything yourself. It’s to notice change. Taking photos of moles you want to track gives you a reliable baseline to compare against next month.
What Happens if a Mole Looks Suspicious
A dermatologist who spots a concerning mole will almost always recommend a biopsy, which means removing all or part of the mole and examining the tissue under a microscope. This is the only way to confirm whether a mole is cancerous. There’s no blood test or imaging scan that can replace it.
For a suspected melanoma, the preferred approach is an excisional biopsy: the entire mole is removed along with a small margin of surrounding skin, going deep enough to include the full thickness of the lesion. Depth matters because the thickness of a melanoma (measured in fractions of a millimeter) determines its stage and guides every treatment decision that follows. The procedure is done under local anesthesia in the office and typically takes less than 30 minutes. Results usually come back within one to two weeks.
For moles that look less concerning, a dermatologist might use a shave biopsy (skimming a thin layer from the surface) or a punch biopsy (taking a small cylindrical core of tissue). These are quicker and leave smaller marks, but they don’t always capture enough depth for a definitive melanoma diagnosis.
Why Early Detection Changes Everything
Melanoma that’s caught while still confined to the skin has a five-year survival rate of 100%, according to data from the National Cancer Institute’s SEER program. Once it spreads to nearby lymph nodes, that drops to 76%. If it reaches distant organs, the rate falls to 34%. Roughly 77% of melanoma cases are caught at the localized stage, which means most people who get diagnosed have an excellent prognosis, precisely because someone noticed a mole that looked wrong.
The U.S. Preventive Services Task Force currently does not recommend for or against routine skin cancer screenings for people without symptoms or risk factors, citing insufficient evidence to weigh the benefits and harms. That recommendation doesn’t apply to anyone who already has a suspicious mole, a history of skin cancer, or a family history of melanoma. For everyone else, monthly self-exams remain the most practical first line of defense.