A melanoma mole typically looks uneven in shape, has irregular or blurred edges, contains multiple colors, and is larger than 6 millimeters (about the size of a pencil eraser). But melanoma doesn’t always follow these rules. Some are tiny, some are pink instead of dark, and some hide under fingernails or on the soles of your feet. Knowing the full range of what melanoma can look like gives you the best chance of catching it early.
The ABCDE Rule
Dermatologists use a five-letter checklist to describe the features that separate melanoma from ordinary moles. Not every melanoma will have all five features, but any one of them is worth paying attention to.
- Asymmetry. If you drew a line through the middle of the mole, the two halves wouldn’t match. Normal moles are roughly symmetrical.
- Border. The edges are ragged, notched, or blurred rather than smooth and well-defined. Pigment may seem to spread or bleed into the surrounding skin.
- Color. Instead of one uniform shade of brown, you see a mix of colors: brown, tan, black, and sometimes patches of white, gray, red, pink, or blue within the same spot.
- Diameter. Most melanomas are larger than 6 millimeters across when diagnosed, roughly the width of a pencil eraser. That said, about 10 to 15 percent of invasive melanomas measure 6 millimeters or smaller, and some Australian studies have found that figure as high as 34 percent. Size alone doesn’t rule melanoma in or out.
- Evolving. The mole has changed in size, shape, color, or texture over the past few weeks or months. New symptoms like itching, pain, or bleeding also count as evolution.
Of these five features, evolving is often the most useful in practice. A mole that has looked the same for years is far less concerning than one that’s visibly different from a month ago.
The Ugly Duckling Sign
Your moles generally look like each other. They share a similar color, size, and shape because they come from the same genetic background. The “ugly duckling” sign is simply the idea that melanoma often stands out as the one mole that doesn’t match the rest. In a study of over 2,000 moles from 80 people, dermatologists were able to accurately flag melanomas by scanning for the outlier among a patient’s full set of moles, and this approach actually reduced unnecessary biopsies compared to evaluating each mole in isolation. When you check your skin, look for the mole that doesn’t belong.
Superficial Spreading Melanoma
This is the most common type, and it’s the one most people picture when they think of melanoma. It grows outward across the skin’s surface before pushing deeper. About half the time, it develops within an existing mole; the other half, it appears as an entirely new spot. Early on, it can be startlingly small. A 1-millimeter black dot, sometimes with a fine scale on top, can already be melanoma in its earliest stage. As it progresses, the borders become more irregular and the colors become more varied, with patches of brown, black, and sometimes blue or red mixing together. This is the type that most reliably follows the ABCDE pattern.
Nodular Melanoma
Nodular melanoma looks quite different from the flat, spreading type. It grows as a firm, dome-shaped bump on the skin, typically larger than 1 centimeter across and raised more than 6 millimeters above the surface. The texture can range from smooth to crusty to rough (sometimes described as cauliflower-like), and it feels hard or firm when you press on it. Color varies widely: it can be black, blue-black, brown, red, pink, or even the same color as your surrounding skin.
This type is particularly tricky because it can look like a blood blister or a harmless bump. It also grows faster than other melanomas, pushing downward into the skin rather than spreading across the surface first. A new, firm, dome-shaped lump that persists for more than a few weeks deserves a closer look.
Melanoma on Palms, Soles, and Nails
Acral lentiginous melanoma shows up in places most people never think to check: the palms of the hands, soles of the feet, and under the nails. On the palm or sole, it starts as a brown or black discoloration that can look like a bruise or a stain. Unlike an actual bruise, it doesn’t fade over time. Instead, it gradually grows larger.
Under a fingernail or toenail, melanoma usually appears as a dark vertical streak running the length of the nail bed. It’s often mistaken for a fungal infection or dried blood from an injury. As it progresses, it can cause the nail to crack or break, and the pigment may spread onto the skin around the nail. That spread of color onto the surrounding skin, known as the Hutchinson sign, is a particularly important warning sign for nail melanoma.
Melanoma Without Dark Color
Roughly 5 percent of melanomas produce little or no pigment. Called amelanotic melanoma, these spots appear pink, red, or skin-toned rather than the dark brown or black most people associate with skin cancer. Because they don’t look like what people expect melanoma to look like, they’re frequently mistaken for a pimple, a scar, or an irritated patch of skin. This often means they’re diagnosed at a later stage, when treatment is more complex. If you have a pink or reddish spot that doesn’t heal within a few weeks, or that slowly grows, it’s worth having a dermatologist examine it.
Changes That Should Prompt a Skin Check
Beyond the visual features, certain physical symptoms signal that a mole needs professional evaluation. Itching, bleeding, crusting, or pain in a mole that was previously painless all count as meaningful changes. A mole that suddenly becomes raised after being flat for years, or one that develops a sore that doesn’t heal, also warrants attention.
The American Academy of Dermatology recommends regular self-exams using a body mole map, which lets you document your spots and track any changes over time. Men over 50 face the highest risk of developing melanoma compared to the general population, but melanoma can occur at any age and on any skin tone. Self-checks work best when you include areas you wouldn’t normally see: your scalp, between your toes, the soles of your feet, and your lower back. A partner or a hand mirror can help with hard-to-see areas.
The simplest rule: if a spot is new, different from your other moles, or changing in any way, have it evaluated. Early-stage melanoma is highly treatable, and the visual signs described above are specifically designed to help you catch it at that stage.