A “bad” mole typically looks different from the rest of your moles in at least one obvious way: it’s uneven in shape, has blurry or jagged edges, contains multiple colors, measures larger than 6 millimeters (about the size of a pencil eraser), or has changed recently. These are the hallmarks of a potentially cancerous mole, and learning to spot them gives you a real advantage, since melanoma caught early has a high survival rate.
The ABCDE Rule
Dermatologists use a five-letter framework to describe what suspicious moles look like. It’s simple enough to use at home during a self-check.
- Asymmetry. One half of the mole doesn’t match the other. A normal mole is roughly symmetrical. If you drew a line down the middle of a concerning mole, the two sides would look like different shapes.
- Border irregularity. The edges are ragged, notched, or blurred rather than smooth and well-defined. The pigment may visibly spread into the surrounding skin, almost like ink bleeding on paper.
- Color variation. Instead of one uniform shade of brown, you see a mix of shades: black, tan, brown, and sometimes areas of white, gray, red, pink, or blue within the same mole.
- Diameter. Most melanomas are larger than 6 millimeters wide, roughly the diameter of a pencil eraser. That said, melanomas can be tiny, so size alone doesn’t rule anything out.
- Evolving. The mole has changed in size, shape, color, or texture over the past few weeks or months. Any noticeable change in a mole is worth paying attention to.
A mole doesn’t need to hit all five criteria to be suspicious. Even one is enough reason to have it looked at.
Physical Symptoms That Signal Trouble
Not every warning sign is purely visual. A mole that starts itching, bleeding, crusting over, or feeling sore and swollen is behaving differently from a normal mole. These physical changes can happen alongside the ABCDE features or on their own. A mole that bleeds without being scratched or injured, or one that develops a scab that won’t heal, deserves prompt attention.
The “Ugly Duckling” Approach
Most people’s moles share a general family resemblance. They tend to be similar in size, shape, and color. The ugly duckling sign is exactly what it sounds like: one mole among many that sticks out and looks obviously different from its neighbors. It might be darker, larger, or just have a different texture. Even if it doesn’t clearly match the ABCDE criteria, a mole that stands apart from the pattern of your other moles is worth having checked.
New Spots Matter More Than Old Moles
Many people assume melanoma develops from a mole they’ve had for years, but the numbers tell a different story. A review of 38 studies covering more than 20,000 melanomas found that 71 percent appeared as entirely new spots on the skin. Only about 29 percent arose from a pre-existing mole. This means monitoring for new spots is just as important as watching your existing moles for changes.
Raised, Firm, and Growing Moles
Nodular melanoma is an aggressive type that doesn’t always follow the ABCDE rules. Instead of spreading outward across the skin, it grows upward and downward. These lesions are often dome-shaped, firm to the touch, and may be dark brown, black, or even skin-colored. They grow noticeably over weeks or months.
Doctors use a separate framework for this type, called the EFG rule: elevated above the skin surface, firm when pressed, and growing progressively. Because nodular melanoma can look like a harmless bump or a blood blister, it’s often caught later than other types. Any new raised spot that feels solid and keeps getting bigger should be evaluated quickly.
Pink or Red Moles Without Pigment
About 5 percent of melanomas don’t look dark at all. Called amelanotic melanoma, these spots appear pink, red, or skin-colored. They can easily be mistaken for a pimple, scar, or irritated patch of skin. Because they lack the dark coloring people associate with skin cancer, they’re frequently diagnosed at a later stage. If you have a pink or reddish spot that persists for several weeks, doesn’t heal, or slowly grows, it’s worth a closer look even though it doesn’t match the classic image of a “bad mole.”
Melanoma on Palms, Soles, and Under Nails
Acral lentiginous melanoma develops in places people rarely think to check: the palms of the hands, the soles of the feet, and underneath fingernails or toenails. On the palms or soles, it starts as a black or brown discoloration that can look like a bruise or stain, but unlike a bruise, it doesn’t fade. Over time, it grows in size.
Under the nails, this type of melanoma appears as dark vertical streaks or bands running the length of the nail bed. It’s sometimes mistaken for a fungal infection or dried blood under the nail. As it progresses, it can cause the nail to crack or break. This is the most common type of melanoma in people with darker skin tones, so checking these areas during self-exams is especially important.
Atypical Moles That Aren’t Cancer
Not every odd-looking mole is melanoma. Atypical moles (also called dysplastic nevi) share some features with melanoma: they can be irregularly shaped, larger than a pencil eraser, and contain a mix of colors including pink, red, tan, brown, and black. They’re often flat with a slightly pebbly or raised center and blurry edges.
The key difference is that atypical moles are stable. They may look unusual, but they aren’t actively changing. Having several atypical moles does increase your overall risk for melanoma, so if your doctor has told you that you have them, more frequent skin checks make sense. The ABCDE criteria still apply: an atypical mole that starts evolving, growing, or developing new colors has crossed from “watch” territory into “get it checked” territory.
How to Do a Self-Check
A thorough skin check takes about 10 minutes and should cover your entire body, including areas you wouldn’t expect: between your toes, the soles of your feet, your scalp, behind your ears, and your lower back. Use a full-length mirror and a hand mirror to see hard-to-reach spots, or ask a partner to help with areas you can’t see yourself.
Take photos of moles you want to track. Comparing a mole to a photo from three or six months ago makes it much easier to notice subtle changes in size, color, or shape than relying on memory alone. Pay attention to any spot that stands out from the rest, any new spot that appeared recently, and any mole that matches one or more of the ABCDE features.