Atypical moles share several visual features that set them apart from ordinary moles: they tend to be asymmetric, larger than 6 millimeters (about the width of a pencil eraser), and display uneven colors or irregular borders. Most people can learn to spot these differences at home using two straightforward methods, though any mole that concerns you warrants a professional evaluation.
The ABCDE Method
The most widely used framework for evaluating a suspicious mole is the ABCDE rule, developed by the National Cancer Institute to describe features of early melanoma and atypical moles.
- Asymmetry. If you drew a line through the middle of the mole, the two halves wouldn’t match. Common moles are typically round or oval and roughly symmetrical.
- Border. The edges look ragged, notched, or blurred rather than smooth and well-defined. Pigment may appear to spread or fade into the surrounding skin.
- Color. Instead of a single uniform shade of brown, the mole contains multiple colors. You might see tan, dark brown, and black within the same spot, or even patches of white, gray, red, pink, or blue.
- Diameter. Most melanomas are larger than 6 millimeters wide, roughly the size of a pencil eraser. That said, atypical moles and melanomas can be smaller, so size alone isn’t a reliable way to rule something out.
- Evolving. The mole has visibly changed over the past few weeks or months in size, shape, color, or elevation. Any new symptom like itching or bleeding also counts.
A mole doesn’t need to check every box to be concerning. Even one or two of these features is worth noting, especially if the mole is evolving.
The “Ugly Duckling” Sign
The ABCDE method evaluates a single mole in isolation. The ugly duckling approach works differently: you compare a mole to all the other moles on your body. Most of a person’s moles tend to look similar to one another in size, color, and shape. An “ugly duckling” is the one that doesn’t fit the pattern.
This method is surprisingly effective even for non-medical professionals. A study published in JAMA Dermatology found that when people with no clinical training used the ugly duckling sign to flag suspicious moles, they achieved 85% sensitivity and 83% specificity for detecting melanoma. Expert dermatologists reached 100% sensitivity with the same approach. In practical terms, the ugly duckling sign catches most melanomas and doesn’t generate an overwhelming number of false alarms.
The two methods complement each other. Use the ugly duckling scan to pick out which moles deserve closer attention, then apply the ABCDE criteria to evaluate those specific spots in detail.
How Atypical Moles Differ From Common Moles
A common mole is small (usually under 5 millimeters), evenly colored, round or oval, and has a clean border. It may be flat or raised, but it looks the same month after month. Most adults have between 10 and 40 common moles.
An atypical mole, sometimes called a dysplastic nevus, is typically larger, with a mix of colors ranging from pink to dark brown. The surface may have both flat and raised areas within the same mole, and the border often fades unevenly into the surrounding skin. Atypical moles tend to appear on the trunk, arms, and legs, though they can show up anywhere.
Having atypical moles doesn’t mean you have cancer. Most atypical moles never become melanoma. But they are a marker of increased risk. Someone with more than five atypical moles has roughly 10 times the melanoma risk of someone with none, according to the National Cancer Institute.
Atypical Moles on Darker Skin
Atypical moles occur far less frequently in people with darker skin tones, at roughly 5% to 21% of the rate seen in fair-skinned individuals. But this lower prevalence creates its own danger. Because both patients and clinicians may not expect to find atypical moles on darker skin, these lesions more commonly appear in areas that aren’t routinely checked, like the palms, soles of the feet, and under the nails. The result is often a delayed diagnosis and a worse outcome.
If you have darker skin, pay particular attention to these less obvious locations during self-exams. The same ABCDE criteria apply, but the color variations may look different against a darker background. Look for spots that are noticeably darker, lighter, or a different texture compared to the surrounding skin.
How to Do a Thorough Self-Exam
Check your skin about once a month, ideally right after a bath or shower. You’ll need a well-lit room, a full-length mirror, and a hand mirror to see your back, scalp, and other hard-to-view areas. A small ruler helps you measure moles and track whether they’re growing.
Work systematically from head to toe. Start with your face and scalp (part your hair to check underneath), then move to the neck, chest, and abdomen. Lift your arms to check the sides of your torso and your underarms. Use the hand mirror to examine your back, buttocks, and the backs of your legs. Finish with the tops and bottoms of your feet, between your toes, and under your fingernails and toenails.
Taking photos of moles you want to monitor makes it much easier to notice subtle changes over time. A mole that looks the same as it did six months ago is far less concerning than one that has shifted in color or grown, even slightly. Photos give you an objective reference point that memory alone can’t provide.
When Moles Run in the Family
Some people inherit a tendency to develop large numbers of atypical moles. Familial atypical multiple mole melanoma syndrome (FAMMM) is characterized by the development of more than 50 atypical moles combined with a personal or family history of melanoma. The moles tend to be larger than 6 millimeters, asymmetric, and unevenly colored.
If you have dozens of unusual-looking moles and a close relative has had melanoma, this pattern is worth discussing with a dermatologist. People with FAMMM typically need more frequent professional skin exams, sometimes every three to six months, and may benefit from full-body photography so their dermatologist can track new or changing lesions between visits.
What Happens if a Mole Looks Suspicious
When a dermatologist evaluates an atypical mole, they’ll often use a dermatoscope, a handheld magnifying device with built-in lighting that reveals structural patterns invisible to the naked eye. Under magnification, the dermatologist looks for specific features like irregular pigment networks, clusters of dots or globules, and uneven coloring patterns. These details help distinguish a harmless but unusual mole from one that needs further evaluation.
If the mole looks concerning, the next step is a biopsy, where a small sample (or the entire mole) is removed and examined under a microscope. The procedure is quick and done under local numbing. Results typically come back within one to two weeks. Most biopsied atypical moles turn out to be benign, but catching the ones that aren’t is exactly the point. Any mole that suddenly changes in size or color, persistently itches, or bleeds should be checked promptly.