The short answer
Most moles are harmless and stay the same for years. The changes worth checking follow the ABCDE guide: Asymmetry, Border irregularity, Color variation, Diameter larger than a pencil eraser, and Evolving (changing). A mole that changes, itches, or bleeds is worth showing a doctor.
Most moles are harmless and do not change.
The ABCDE guide flags moles worth checking: Asymmetry, Border, Color, Diameter, Evolving.
A mole that changes, itches, or bleeds is worth a doctor's look.
A new or changing spot in adulthood deserves attention.
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The full explanation.
The simple version
Most people have moles, and almost all of them are harmless. A mole that is new, changing, or looks different from your other moles is the pattern worth checking. Doctors use a simple checklist called the ABCDE rule to describe what to look for.
The ABCDE rule
Asymmetry: one half of the mole does not match the other half. Border: the edges are ragged, notched, or blurry instead of smooth. Color: the mole has more than one color, or an uneven color, rather than one even shade. Diameter: melanoma is usually larger than 6 millimeters across, about the size of a pencil eraser, though it can be smaller. Evolving: the mole is changing in size, shape, or color over time. Any one of these features is worth a doctor's look, and having more than one raises the concern further.
The "ugly duckling" idea
Many dermatologists also look for the mole that simply does not match the others. Most people's moles tend to look similar to each other, like siblings. A mole that stands out from that pattern, even without every ABCDE feature, is worth pointing out during a skin check.
Far more common, harmless changes
Moles can naturally darken slightly with sun exposure, and new moles can appear during childhood, pregnancy, or teenage years. These are usually a uniform color, round or oval, and stable over months to years. A mole that has looked exactly the same for years is reassuring, even if it has one unusual feature, though any new change is still worth mentioning at your next skin check.
What a doctor checks next
A dermatologist examines the mole, often with a handheld magnifying tool called a dermatoscope, which shows detail not visible to the naked eye. If a mole raises concern, the doctor performs a skin biopsy. This can be a shave biopsy, using a small blade to remove the top of the growth, or an excisional biopsy, which removes the entire growth with a scalpel. The sample goes to a lab, where a pathologist checks it under a microscope. If it is melanoma, the report includes the tumor's thickness, called Breslow thickness, which is one of the main factors doctors use to plan treatment. NCI says the pathologist typically sends the report to your doctor within 10 days after the biopsy or surgery.
What a normal skin check does not rule out
A skin check by eye, even by an experienced dermatologist, cannot catch everything with certainty, which is why any mole you are personally worried about is worth mentioning directly, even if the doctor does not flag it first. You know your own skin better than anyone else in the room.
When to get help sooner
Nothing about a mole calls for an ambulance. Speed here means weeks, not minutes.
- Call your care team the same day if a mole is bleeding on its own, weeping, or has broken into a sore that will not close over.
- Call your care team within a day or two if a spot has visibly shifted in size, shape, or colour over a few weeks, itches or stings without letting up, looks unlike every other mole you have, or is brand new on skin that is past its thirties.
What to ask your doctor
- Can you check this mole [describe location and changes]?
- Should I have a full-body skin exam?
- How often should I have my skin checked given my risk factors?
- Should this be biopsied, or can we watch it?
Sources
Words to know
Tap any term to see what it means.
Common questions
Are most moles cancer?
No. Most moles are harmless and stay the same for years. It is changing or unusual moles that are worth checking.
What is the ABCDE guide?
It flags moles worth checking: Asymmetry, Border irregularity, Color variation, Diameter over about 6 mm, and Evolving (any change over time).
What changes should I watch for?
A mole that grows, changes color or shape, itches, bleeds, or does not heal — or a new dark spot in adulthood — is worth a doctor's look.
How is skin checked?
A doctor or dermatologist can examine the skin and, if needed, take a small sample (biopsy) of a suspicious mole.
Questions to ask your doctor
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Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-18Next planned review: 2027-08-03
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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