Cancerous moles typically look uneven in shape, color, or border compared to normal moles. A normal mole is usually round, one solid color, and smaller than 6 millimeters (about the size of a pencil eraser). A mole that could be melanoma breaks one or more of those rules: it’s lopsided, has ragged edges, contains multiple colors, grows larger than 6 millimeters, or changes noticeably over weeks to months.
The ABCDE Rule for Spotting Melanoma
The most widely used method for evaluating a suspicious mole is the ABCDE rule, developed by the National Cancer Institute. Each letter flags a specific visual warning sign.
- Asymmetry. If you drew a line through the middle of the mole, the two halves wouldn’t match. Normal moles are roughly symmetrical.
- Border irregularity. The edges look ragged, notched, or blurred rather than smooth. Pigment may spread or fade into the surrounding skin.
- Color variation. Instead of one uniform shade, the mole contains a mix of brown, tan, and black. You may also see patches of white, gray, red, pink, or blue within the same spot.
- Diameter. Most melanomas are larger than 6 millimeters wide, roughly the size of a pencil eraser. That said, melanomas can start smaller, so size alone isn’t enough to rule one 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 attention.
A mole doesn’t need to hit all five criteria to be suspicious. Even one of these features, especially evolution, is reason enough to have it examined.
How a Cancerous Mole Differs From an Atypical Mole
Not every odd-looking mole is cancer. Atypical moles (sometimes called dysplastic nevi) are common and share some features with melanoma, which makes telling them apart tricky. Both can be larger than 5 millimeters, have irregular borders, and contain mixed colors. The differences are subtle but important.
Atypical moles tend to have a smooth, slightly scaly, or pebbly surface and a border that gently fades into the surrounding skin. Their color range is usually limited to pink, tan, and brown. Melanoma, by contrast, is more likely to contain stark color contrasts, including areas of black, blue, white, or gray. The shape is often clearly asymmetrical rather than just slightly irregular. And perhaps the most telling difference is the surface: a melanoma may break down and look scraped, become hard or lumpy, or begin to ooze and bleed. Atypical moles generally stay stable once they’ve formed.
Having many atypical moles does increase your melanoma risk, so regular skin checks matter more if that applies to you.
The “Ugly Duckling” Sign
Beyond the ABCDE rule, there’s a simpler visual test. Look at the moles on your body as a group. Most of your moles probably share a general “family resemblance,” similar in size, shape, and color. A mole that stands out from the rest, the ugly duckling, deserves closer attention. This approach is especially useful when a mole doesn’t clearly meet the ABCDE criteria but still looks different from everything around it.
Changes That Signal Progression
Early melanoma is often flat and painless, which is why it’s easy to ignore. The physical symptoms that most people associate with something being “wrong” tend to show up later. Watch for a mole that starts itching when it never did before, bleeds without being scratched or bumped, or develops a crust or scab that keeps coming back. A mole that was flat and begins to feel raised or lumpy is also changing in a significant way.
These changes can happen over weeks or months. Taking periodic photos of moles you’re keeping an eye on gives you a reliable comparison point, since gradual changes are hard to notice in real time.
When Skin Cancer Doesn’t Look Like a Mole
About 5 percent of melanomas don’t contain the dark pigment most people expect. These amelanotic melanomas appear pink, red, or skin-colored, making them easy to confuse with a pimple, bug bite, or scar. Because they look so innocuous, they’re often diagnosed at a later stage than pigmented melanomas. A pink or red bump that persists for several weeks, especially if it’s firm or slowly growing, should be evaluated.
Basal cell carcinoma, the most common type of skin cancer, also doesn’t look like a typical mole. It often appears as a shiny, translucent bump that looks pearly white or pink on lighter skin and brown or glossy black on darker skin. Tiny blood vessels may be visible on the surface. Other forms show up as a flat, scaly patch, a waxy scar-like area with no clear border, or a sore that heals and then reopens. Any wound that won’t fully heal over several weeks is a classic warning sign.
Skin Cancer in Hidden Locations
Melanoma can develop in places you’d never think to check. Acral lentiginous melanoma appears on the palms of the hands, soles of the feet, or under fingernails and toenails. On the hands and feet, it starts as a brown or black discoloration that looks like a bruise or stain but gradually grows. Under a nail, it typically appears as a dark vertical streak running the length of the nail bed. As it progresses, the nail may crack, break, or lift. This form is sometimes mistaken for a fungal infection or an old blood blister, which delays diagnosis.
These locations get less sun exposure, which is why people overlook them. A complete skin self-check should include the spaces between your toes, the soles of your feet, your nail beds, and your palms.