A cancerous mole typically looks different from your other moles in at least one noticeable way: it may be asymmetrical, have uneven color, show irregular borders, or change over time. But skin cancer doesn’t always follow the textbook description, and some forms look nothing like a dark mole at all. Knowing the full range of what to watch for can help you catch something early.
The ABCDE Rule for Melanoma
The most widely used framework for spotting melanoma is the ABCDE rule, developed by the National Cancer Institute. Each letter describes a visual feature of a suspicious mole:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles tend to be roughly symmetrical.
- Border irregularity: The edges look ragged, notched, or blurred rather than smooth. Pigment may appear to bleed into the surrounding skin.
- Color variation: Instead of one uniform shade of brown, the mole contains multiple colors. You might see black, tan, brown, white, gray, red, pink, or blue within the same spot.
- Diameter: Most melanomas are larger than 6 millimeters across (roughly the size of a pencil eraser) at the time of diagnosis. However, about 25 to 33 percent of melanomas are smaller than 6 millimeters, so size alone is not a reliable way to rule one out.
- Evolving: The mole has changed in size, shape, or color over weeks or months. Any new or shifting feature in an existing mole is worth attention.
A mole doesn’t need to check every box. A single suspicious feature, especially evolution, is enough reason to have it examined.
The “Ugly Duckling” Sign
Beyond the ABCDE criteria, one of the simplest ways to spot a problem is the ugly duckling sign. Most of your moles share a general “family resemblance” in color, size, and shape. If one mole stands out as clearly different from the rest, that outlier deserves closer inspection, even if it doesn’t obviously meet any single ABCDE criterion.
Nodular Melanoma Looks Different
Not all melanomas spread outward like a flat, irregular patch. Nodular melanoma grows downward into the skin and can develop faster than other types. It often appears as a raised, dome-shaped bump that is firm to the touch and grows noticeably over weeks. It may be dark brown, black, blue, or even skin-colored. Because it can look symmetrical and have smooth borders, it sometimes doesn’t trigger the standard ABCDE warnings.
For this type, doctors use a separate set of criteria called EFG: elevated above the skin surface, firm when pressed, and growing progressively. If you notice a new raised bump that feels solid and is getting bigger, that pattern alone warrants a professional look.
Melanoma Without Dark Pigment
About 5 percent of melanomas are amelanotic, meaning they lack the dark pigment most people associate with skin cancer. These appear as pink, red, or skin-colored spots that can easily be mistaken for a pimple, bug bite, or minor irritation. Because they don’t look like what most people picture when they think “cancerous mole,” amelanotic melanomas are often diagnosed at a later stage. If you have a pink or reddish spot that persists for more than a few weeks and doesn’t respond to typical wound healing, it’s worth having checked.
Skin Cancer on Palms, Soles, and Nails
Acral lentiginous melanoma appears in places people rarely think to check: the palms of the hands, soles of the feet, and under the nails. It’s the most common form of melanoma in people of color. On the palm or sole, it starts as a black or brown discoloration that can look like a bruise or stain, but unlike a bruise, it grows in size over time rather than fading.
Under a nail, this type of melanoma (called subungual melanoma) shows up as a dark vertical streak running the length of the nail bed. It’s sometimes mistaken for a fungal infection or dried blood under the nail. A few features help distinguish it from a simple bruise: a bruise under the nail usually appears quickly after an injury and gradually grows out as the nail grows, while melanoma develops slowly and doesn’t move with nail growth. One important warning sign, known as Hutchinson’s sign, is when the dark pigment spreads from under the nail onto the surrounding skin of the fingertip or cuticle.
Other Types of Skin Cancer
Melanoma gets the most attention, but two other skin cancers are far more common, and they look quite different from a typical mole.
Basal Cell Carcinoma
This is the most common form of skin cancer. On lighter skin, it often appears as a firm, raised, round bump with a shiny or pearly surface, sometimes pink or red. On darker skin, the same bump tends to look brown, black, or blue. Some basal cell carcinomas develop a dip or crater in the center that may scab over and bleed. Others look like a rough, scaly patch that resembles a freckle or age spot but feels textured. A sore that heals and then returns, or one that simply won’t heal at all, is another classic presentation.
Squamous Cell Carcinoma
This type often presents as a firm nodule or a flat sore with a scaly, crusty surface. It can be skin-colored, pink, red, brown, or black depending on skin tone. On the lip, it may start as a rough, scaly patch that eventually opens into a sore. A new sore or raised area that develops on top of an old scar is another common pattern. Some squamous cell carcinomas look wart-like, with a rough, bumpy texture.
How to Check Your Own Skin
A monthly self-exam, ideally after a shower when your skin is fully visible, is a practical habit. Use a full-length mirror and a hand mirror to check areas you can’t see directly: your back, the backs of your legs, your scalp (a blow dryer can help part the hair), and between your toes. Don’t skip the soles of your feet, your palms, your nail beds, and your ears.
What you’re looking for isn’t a single dramatic warning sign. You’re looking for change. A mole that’s darker than it used to be, a new spot that wasn’t there a few months ago, a bump that’s getting bigger, a sore that won’t heal. Take photos of moles you want to track so you have a baseline for comparison. If something looks off or different from your usual pattern of spots and moles, a dermatologist can evaluate it quickly, and early detection makes a significant difference in outcomes.