Cancerous moles typically share a set of visible warning signs: uneven shape, irregular borders, multiple colors, a diameter larger than 6 millimeters (about the size of a pencil eraser), and noticeable changes over weeks or months. But not all skin cancers look the same, and some barely resemble a mole at all. Knowing the full range of what to look for can help you spot something suspicious early, when treatment is most effective.
The ABCDE Rule for Melanoma
The most widely used framework for identifying melanoma is the ABCDE rule, developed by the National Cancer Institute. Each letter flags a specific visual feature:
- Asymmetry. One half of the mole doesn’t match the other. Normal moles are roughly symmetrical.
- Border. The edges are ragged, notched, or blurred rather than smooth. Pigment may spread into the surrounding skin.
- Color. Instead of a single uniform shade, the mole contains a mix of colors: black, brown, tan, and possibly areas of white, gray, red, pink, or blue.
- Diameter. Most melanomas are larger than 6 millimeters wide, about the width of a pencil eraser. They can be smaller, but a growing spot that crosses that threshold deserves attention.
- Evolving. The mole has changed in size, shape, or color over the past few weeks or months. Any visible change in a previously stable mole is a red flag.
A mole doesn’t need to check every box to be concerning. Even one or two of these features, especially evolving, is reason enough to have it examined.
Atypical Moles vs. Melanoma
Plenty of harmless moles look a little odd. These are called dysplastic nevi, or atypical moles, and they can overlap with melanoma in confusing ways. Both can be wider than 5 millimeters, have irregular edges, and contain mixed colors. The key differences come down to degree and texture.
An atypical mole tends to be flat with a smooth or slightly pebbly surface. Its colors lean toward pink, tan, and brown. It may have a fuzzy border that fades into the surrounding skin, but it stays stable over time. Melanoma, by contrast, is more likely to contain darker or more varied colors, including black and blue. Its surface may break down, becoming hard, lumpy, or scabbed. It may ooze or bleed without being scratched or injured. And critically, it changes. A mole that looked the same five years ago and looks the same today is far less worrying than one that shifted shape last month.
The Ugly Duckling Sign
Beyond examining individual moles, it helps to compare them to each other. Most of your moles probably share a general “family resemblance” in size, shape, and color. The ugly duckling sign refers to a mole that stands out from the rest, the one that looks noticeably different from its neighbors. Even if it doesn’t clearly meet the ABCDE criteria, a mole that simply doesn’t match the pattern of your other moles warrants a closer look.
Nodular Melanoma Looks Different
Not all melanomas spread outward across the skin first. Nodular melanoma grows downward into the skin, which makes it more aggressive and harder to catch with the standard ABCDE framework. Instead, it follows a different set of warning signs known as the EFG rule:
- Elevated. The lesion is raised above the skin surface.
- Firm. It feels solid to the touch rather than soft or squishy.
- Growing. It increases in size over weeks or months.
Nodular melanoma can appear as a dome-shaped bump that’s dark brown, black, or even skin-colored. Because it may not have the ragged borders or color variation people associate with melanoma, it’s easier to dismiss. A firm, raised bump that’s actively growing is worth getting checked regardless of its color.
Melanoma Without Color
One of the trickiest forms of skin cancer is amelanotic melanoma, which contains little or no pigment. Instead of the dark brown or black spot most people picture, it often appears as a pink to red bump, flat patch, or fleshy nodule. Because it lacks the classic dark coloring, people frequently mistake it for a pimple, scar, or minor skin irritation. The key giveaway is persistence. A pink or reddish spot that doesn’t heal, continues to grow, or bleeds without explanation should be evaluated.
Skin Cancer on Palms, Soles, and Nails
Acral lentiginous melanoma is a form of skin cancer that develops only on the palms of the hands, soles of the feet, or under the nails. It appears as an unevenly pigmented black or brown spot that looks different from the surrounding skin and grows over time. Under a nail, it often shows up as a dark streak or band of color running from the cuticle to the tip of the nail.
This type of melanoma is particularly important for people with darker skin tones. While skin cancer overall is less common in people with darker skin, acral lentiginous melanoma accounts for a disproportionate share of melanoma cases in Black, Hispanic, and Asian populations. It’s often diagnosed late because people don’t think to examine these hidden areas, and the standard ABCDE criteria don’t apply well to spots on palms, soles, and nail beds. A screening tool called CUBED (Color, Uncertain diagnosis, Bleeding, Enlargement, Delay in healing) is more useful for these locations. Bleeding, discomfort while walking, or a spot that simply won’t heal are common reasons people eventually seek care.
What Basal Cell Carcinoma Looks Like
Melanoma gets the most attention, but basal cell carcinoma is the most common form of skin cancer. It doesn’t look like a mole at all. On lighter skin, it typically appears as a slightly transparent or pearly bump that’s pink or skin-colored. You may be able to see tiny blood vessels through the surface. On darker skin tones, it often looks like a brown or glossy black bump with a rolled, raised border.
Basal cell carcinoma can also take less obvious forms: a flat, scaly patch with a slightly raised edge, a brown or blue lesion with dark spots and a translucent border, or a white, waxy area that resembles a scar. These bumps and patches tend to bleed easily and scab over, then reopen. A sore that cycles between bleeding and scabbing without fully healing is one of the most reliable warning signs.
What to Watch For Over Time
The single most useful habit for catching skin cancer early is paying attention to change. A mole that’s been the same size, shape, and color for years is almost certainly benign, even if it’s large or slightly irregular. What matters most is a spot that’s new, growing, bleeding, or shifting in appearance. Monthly self-checks improve your chances of catching something early. Take photos of any moles you’re unsure about so you have a baseline for comparison. Pay particular attention to sun-exposed areas like your face, neck, arms, and upper back, but don’t skip the less obvious spots: between your toes, on your scalp, under your nails, and on the soles of your feet.