A suspicious mole typically shows one or more of five visual warning signs: asymmetry, irregular borders, uneven color, a diameter larger than 6 millimeters (about the size of a pencil eraser), or noticeable changes over weeks to months. These are the basics, but the full picture is more nuanced. Some dangerous moles break the rules entirely, appearing small, pink, or otherwise unremarkable. Knowing what to look for, and what can fool you, is the best way to catch a problem early.
The ABCDE Rule
Dermatologists use five visual features to flag moles that need a closer look. The National Cancer Institute calls this the ABCDE rule, and it covers the most common signs of early melanoma:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles tend to be roughly symmetrical.
- Border: The edges are ragged, notched, or blurred rather than smooth. Pigment may spread into the surrounding skin.
- Color: The mole contains multiple shades, such as black, brown, and tan mixed together. Areas of white, gray, red, pink, or blue can also appear.
- Diameter: The mole is wider than about 6 millimeters, roughly the width 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.
A mole doesn’t need to check every box. Even one of these features is enough to warrant a professional evaluation. And “evolving” is arguably the most important of the five, because any mole that is actively changing deserves attention regardless of what it looks like right now. As one MD Anderson Cancer Center dermatologist put it, seeing changes over weeks to months is a cause for concern.
The Ugly Duckling Sign
If you have many moles or freckles, the ABCDE rule can feel overwhelming to apply to each one individually. That’s where the “ugly duckling” approach helps. Instead of analyzing each mole in isolation, you compare them to each other. Most of your moles will share a general look: similar size, color, and shape. The one that doesn’t match, the outlier that’s darker, larger, more raised, or just different, is the one to pay attention to.
This technique works especially well for people with dozens of moles, where trying to judge every single one against the ABCDE criteria would be impractical. It’s a pattern-recognition shortcut that dermatologists themselves use during skin exams.
Symptoms You Can Feel
Not all warning signs are visual. A mole that starts itching, becomes tender, or bleeds without being scratched or bumped is worth getting checked. The Mayo Clinic lists new itchiness, pain, bleeding, and inflammation as changes that should prompt a visit to your doctor. These sensory symptoms can sometimes appear before the mole looks obviously different, making them an early signal that something is changing beneath the surface.
Moles That Don’t Look Like Moles
About 5 percent of melanomas are what’s called amelanotic, meaning they lack the dark pigment most people associate with skin cancer. These appear as pink, red, or skin-colored spots. Memorial Sloan Kettering Cancer Center notes that because they’re easily confused with harmless bumps or irritation, amelanotic melanomas are often diagnosed at a later stage than their darker counterparts. If you have a pinkish spot that doesn’t heal, grows slowly, or just doesn’t seem right, it’s worth having it examined even though it doesn’t fit the typical “dark mole” image.
Melanoma Under the Nails
Melanoma can also develop under a fingernail or toenail, where it typically appears as a dark vertical streak running from the base to the tip. The line is usually brown or black and may start narrow, under 3 millimeters wide, then gradually widen or multiply. Over time, the discoloration can spread to the cuticle and cover the entire nail. Other signs include the nail splitting, cracking, lifting away from the nail bed, or developing a small irregularly shaped bump underneath. This type of melanoma is more common on the thumb and big toe, and it’s particularly important to watch for on darker skin tones, where it occurs at higher rates relative to other melanoma types.
What Normal Moles Look Like
Knowing what’s normal makes it easier to spot what isn’t. A typical benign mole is a single uniform color (usually tan or brown), has smooth and well-defined edges, and is round or oval. It may be flat or slightly raised. Most people develop new moles through their 20s and 30s, and existing moles can slowly change with age, sometimes becoming lighter or slightly raised over decades. These gradual, predictable shifts are different from the rapid changes over weeks or months that signal concern.
One common mimic of melanoma is a seborrheic keratosis, sometimes called a “barnacle” or age spot. These can look dark, rough, and irregular, which understandably alarms people. Under magnification, dermatologists can distinguish them by the presence of tiny cyst-like structures and pore-like openings on the surface, features melanoma doesn’t have. But this distinction is often impossible with the naked eye, which is why anything that looks off is reasonable to have checked rather than dismissed.
How to Do a Self-Check
A monthly skin self-exam is the simplest way to catch changes early. You’re looking for anything new, anything different, and anything that matches the warning signs described above. Here’s a practical approach:
- Use a well-lit room and a full-length mirror. A hand mirror helps for your back, scalp, and behind your ears.
- Check everywhere, including between your toes, the soles of your feet, your palms, under your nails, and your scalp (a blow dryer can help part your hair).
- Photograph moles that you want to track. Comparing photos month to month makes subtle changes much easier to spot than relying on memory alone.
- Apply the ugly duckling rule first, then look more closely at any outliers using the ABCDE criteria.
No major U.S. medical organization currently recommends a specific schedule for professional skin exams for the general population, because the evidence on universal screening is still inconclusive. That said, people with risk factors (a history of sunburns, many moles, fair skin, family history of melanoma, or a personal history of skin cancer) benefit from regular professional skin checks at a frequency their dermatologist recommends based on their individual risk.
What Happens If Your Mole Looks Suspicious
The only way to know for certain whether a mole is cancerous is a biopsy, where a small sample of tissue is removed and examined under a microscope. There are a few different methods depending on the situation. A shave biopsy takes a thin layer from the surface and is the most common type. A punch biopsy uses a small circular tool to remove a deeper, pencil-eraser-sized core of skin. If melanoma is suspected, an excisional biopsy is usually preferred, where the entire mole and a small margin of surrounding skin are removed with a scalpel and the site is closed with stitches.
The procedure is done under local anesthesia, typically in a dermatologist’s office, and takes only a few minutes. Results usually come back within one to two weeks. If the biopsy is benign, no further treatment is needed. If melanoma is found, the depth and stage of the cancer determine the next steps, but catching it early, before it grows deep into the skin, dramatically improves outcomes.