Most moles are not cancerous. The average adult has between 10 and 40 common moles, and the vast majority will never become melanoma. That said, about 25% of melanomas do develop from an existing mole, while the remaining 75% appear as entirely new spots on the skin. Knowing what to look for can help you catch a problem early, when melanoma is most treatable.
The ABCDE Warning Signs
Dermatologists use a five-letter checklist to evaluate whether a mole looks suspicious. These features describe early melanoma:
- Asymmetry: One half of the mole doesn’t match the other half in shape.
- Border: The edges are ragged, notched, or blurred rather than smooth and well-defined. The pigment may spread into the surrounding skin.
- Color: The mole has multiple shades or colors. A mix of black, brown, tan, white, gray, red, pink, or blue within a single spot is concerning.
- Diameter: The mole is wider than 6 millimeters, roughly the size of a pencil eraser. Melanomas can be smaller than this, but most are at or above that threshold.
- Evolving: The mole has changed in size, shape, color, or height over recent weeks or months. New symptoms like bleeding, itching, or crusting also count.
No single feature on its own confirms cancer. A mole can be large and still be harmless, or small and still be melanoma. The more of these features a mole has, the more reason to get it checked.
The “Ugly Duckling” Sign
If you have many moles or freckles, there’s another approach that can be even more intuitive than the ABCDE checklist. Look for the one spot that doesn’t match the rest. Maybe it’s darker than your other moles, more raised, scabbed over, or just visually different. Dermatologists call this the “ugly duckling” sign, and it’s a useful way to flag a suspicious spot when you already have a lot of moles to compare against.
Atypical Moles vs. Melanoma
Not every unusual-looking mole is cancer. Some people have what are called atypical moles (also known as dysplastic nevi), which share a few visual traits with melanoma but are not cancerous. Atypical moles tend to be wider than 5 millimeters, may have irregular or notched edges, and often contain a mixture of tan, brown, and pink shades. They can look alarming, but only rarely does one actually turn into melanoma.
There are important differences between the two. Atypical moles typically have a smooth or slightly pebbly surface, while melanoma may break down and look scraped, become hard or lumpy, or ooze and bleed. Melanoma also tends to have a wider range of colors, including areas of white, gray, or blue that are uncommon in atypical moles. And once an atypical mole is fully removed, it doesn’t come back. Melanoma sometimes does.
Having atypical moles does raise your overall melanoma risk, though. Someone with more than five atypical moles has roughly 10 times the melanoma risk of someone with none. That doesn’t mean those specific moles will become cancer. It means people with many atypical moles benefit from more frequent monitoring.
How a Suspicious Mole Gets Diagnosed
The only way to know for certain whether a mole is cancerous is through a biopsy, where a small sample of tissue is removed and examined under a microscope. There are a few ways this is done, and which one your dermatologist chooses depends on the size and depth of the spot.
A shave biopsy scrapes off the top layers of skin with a scalpel or razor. It’s quick and typically doesn’t require stitches. A punch biopsy uses a small circular tool to remove a deeper core of tissue, including layers beneath the surface. This one may need a stitch or two. An excisional biopsy removes the entire mole along with a border of healthy skin around it. It’s the most thorough option and generally requires stitches to close the wound.
Before a biopsy, your dermatologist will likely examine the mole using a dermatoscope, a handheld magnifying device with its own light source. This tool reveals structures beneath the skin’s surface that aren’t visible to the naked eye. Studies show that adding dermatoscopy to a visual exam increases detection sensitivity for melanoma from about 80% to over 92%, making it significantly more reliable than eyeballing alone.
Why Change Matters Most
Of all five ABCDE features, the “E” for evolving is often the most important in practice. A mole that has looked the same for years is far less concerning than one that’s recently grown, darkened, or started behaving differently. Any change in size, shape, color, or elevation is worth attention. So is a mole that begins to itch, crust, or bleed when it never did before.
This is why knowing your own skin matters. You’re more likely to notice a change in one of your moles than a doctor who sees you once a year. Taking photos of moles you want to track can make it easier to spot gradual shifts that you might otherwise miss.
Who Faces Higher Risk
Some people are more likely to develop melanoma than others. Having a large number of common moles (50 or more) increases your baseline risk. Having multiple atypical moles raises it further. A personal or family history of melanoma, fair skin that burns easily, a history of severe sunburns, and heavy UV exposure (including tanning beds) all contribute.
Interestingly, no major medical organization in the U.S. currently recommends routine skin cancer screening for people without risk factors or symptoms. The U.S. Preventive Services Task Force has found insufficient evidence to recommend universal visual skin exams. But this recommendation explicitly does not apply to people with a personal or family history of skin cancer, or to anyone who has noticed a changing or irregular mole. For those individuals, professional evaluation is clearly warranted.