Most moles are harmless, but a few specific visual clues can help you distinguish a normal mole from one that needs medical attention. The most reliable method is the ABCDE rule, a set of five characteristics developed at a National Institutes of Health consensus conference and used by dermatologists worldwide. Knowing these signs, along with a few lesser-known red flags, gives you a practical framework for deciding when to get a mole checked.
The ABCDE Rule
Each letter stands for a feature that, when present, raises the likelihood a mole could be melanoma.
- Asymmetry. If you drew a line through the middle of the mole, the two halves wouldn’t match. Normal moles tend to be roughly symmetrical.
- Border irregularity. The edges look ragged, notched, or blurred rather than smooth. Pigment may seem to bleed into the surrounding skin.
- Color variation. Instead of one uniform shade of brown, you see a mix of brown, tan, black, or even patches of white, gray, red, pink, or blue within the same mole.
- Diameter. Most melanomas are larger than 6 millimeters when diagnosed, roughly the size of a pencil eraser. However, melanomas can absolutely be smaller than this. The American Academy of Dermatology and the American Cancer Society both caution that the diameter guideline can be misleading, and no suspicious mole should be dismissed just because it’s small.
- Evolving. Any change in size, shape, color, or texture over weeks or months is a warning sign. A mole that starts itching, bleeding, or crusting also counts as evolving.
You don’t need all five features to be concerned. A single one, especially “E” for evolving, is enough reason to have a dermatologist take a look.
The Ugly Duckling Sign
Most of your moles probably look similar to each other in size, shape, and color. The “ugly duckling” sign is simple: if one mole stands out as noticeably different from everything else on your skin, that outlier deserves attention. This approach is especially useful when a mole doesn’t clearly meet the ABCDE criteria but still looks “off” compared to its neighbors. Your gut instinct that something doesn’t belong is often worth acting on.
Moles That Don’t Look Like Moles
Not every dangerous skin lesion is a dark, irregularly shaped mole. Some melanomas produce little or no pigment. These amelanotic melanomas often appear as a pink, red, or skin-colored bump or flat spot, making them easy to mistake for a pimple, a scar, or an insect bite that won’t go away. Because they don’t trigger the usual “dark and irregular” alarm bells, they tend to be diagnosed at a more advanced stage. Any new, persistent pink or red spot on your skin that doesn’t heal within a few weeks is worth showing to a doctor.
Basal cell carcinoma, the most common type of skin cancer, also doesn’t look like a typical mole. It can appear as a shiny, pearly bump (sometimes translucent), a flat scaly patch, or a sore that repeatedly heals and reopens. On darker skin tones, it may look brown or glossy black with tiny visible blood vessels. A white, waxy, scar-like area with no clear border is another presentation. These lesions grow slowly and rarely spread to other parts of the body, but they can cause significant local damage if left untreated.
Check Places You Wouldn’t Expect
Melanoma doesn’t only show up on sun-exposed skin. A subtype called acral melanoma forms on the palms of your hands, the soles of your feet, or under your fingernails and toenails. It is not believed to be caused by sun exposure, which is part of why people overlook it. Watch for a dark spot, patch, or discoloration on your palms or soles, or a dark vertical streak running through a nail bed. These streaks can eventually cause the nail to crack or break. Any growing, changing, or painful spot in these locations warrants prompt evaluation.
How Fast Can a Mole Change?
There’s no single timeline. Some melanomas spread within a few months, while others, particularly a type called lentigo maligna melanoma, can grow over decades with barely noticeable changes. This unpredictability is exactly why regular self-checks matter. The American Cancer Society recommends performing a head-to-toe skin self-exam once a month. People at higher risk (those with many moles, a family history of skin cancer, a personal history of skin cancer, or a weakened immune system) should talk with their doctor about whether more frequent checks or professional skin exams make sense.
When you do a self-exam, use a full-length mirror and a hand mirror to check your back, scalp, and the backs of your legs. Don’t skip between your toes, behind your ears, or your genital area. Taking photos of moles you want to track makes it much easier to spot subtle changes month to month.
What Happens If You Get a Mole Checked
A dermatologist’s first tool is a dermoscope, a handheld magnifying device with a special light that reveals structures beneath the skin’s surface invisible to the naked eye. This matters more than you might think: the accuracy of diagnosing melanoma with the unaided eye is only about 60%. Dermoscopy, when used by an experienced examiner, improves that accuracy by roughly 49%. In the hands of someone without training, however, it performs no better than a visual check alone, which is one reason seeing a board-certified dermatologist specifically makes a difference.
If the mole looks suspicious under dermoscopy, the next step is a biopsy, where a small sample of tissue is removed and sent to a lab. There are three common types:
- Shave biopsy. A blade removes the top layers of skin. No stitches needed. Used for surface-level concerns.
- Punch biopsy. A small circular tool removes a deeper core of skin, sometimes including the fat layer beneath. May require a stitch or two depending on size.
- Excisional biopsy. The entire mole and a border of healthy skin around it are cut out with a scalpel. This typically requires stitches and is often chosen when melanoma is strongly suspected.
The procedure is done with local numbing and usually takes only a few minutes. Results typically come back within one to two weeks. A biopsy is the only way to definitively determine whether a mole is cancerous. No visual check, no matter how experienced the doctor, replaces a lab analysis when there’s real concern.