Melanoma typically appears as an unusual mole or spot on the skin that looks different from your other moles. It often has an irregular shape, uneven color, and a diameter larger than 6 millimeters (about the size of a pencil eraser). But melanoma doesn’t always follow these rules, and some forms look nothing like a dark mole at all.
The ABCDE Rule for Spotting Melanoma
The most widely used framework for identifying melanoma is the ABCDE rule, which breaks down the five visual features that set melanoma apart from ordinary moles:
- Asymmetry: One half of the spot doesn’t match the other half. Normal moles tend to be roughly symmetrical.
- Border irregularity: The edges are ragged, notched, or blurred rather than smooth. The pigment may bleed into the surrounding skin.
- Color variation: Instead of one uniform shade, melanoma often contains a mix of brown, black, and tan. 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, though they can start smaller. Any mole that’s growing deserves attention regardless of its current size.
- Evolving: The spot has changed in size, shape, or color over the past weeks or months, or it has started bleeding or itching.
No single feature on its own confirms melanoma. A spot with two or three of these characteristics is more concerning than one with just a single trait. And some melanomas, especially in their earliest stages, may only show one subtle change.
The “Ugly Duckling” Sign
Your moles generally resemble one another. They share a similar color palette, size range, and overall pattern. Melanoma often breaks that pattern. A 1998 observation that became known as the “ugly duckling” sign describes a lesion that simply looks different from all the others on your body. If one mole stands out as the odd one, that alone is a reason to have it evaluated, even if it doesn’t clearly match every letter of the ABCDE criteria.
Superficial Spreading Melanoma
This is the most common type, and it’s what most people picture when they think of melanoma. It usually appears as a flat or slightly raised spot with uneven borders and color variations. It tends to grow outward across the skin surface before it grows deeper, which means it often starts as a slowly expanding patch of mixed brown, black, or tan tones. It can develop anywhere on the body but is especially common on the trunk in men and on the legs in women.
Nodular Melanoma
Nodular melanoma looks and behaves very differently from the flat, spreading type. It grows as a firm, dome-shaped bump that may be black, blue-black, red, pink, brown, or even your natural skin tone. The texture can range from smooth to crusty or rough, sometimes resembling cauliflower. Some people describe it as looking like a blood blister that won’t go away.
These growths are typically larger than 1 centimeter across (about the length of a staple) and feel hard or firm when you press on them. Because nodular melanoma grows downward into the skin rather than spreading outward, it’s more aggressive and often diagnosed at a later stage. It also doesn’t follow the ABCDE criteria as neatly. A symmetrical, evenly colored bump that’s firm and growing quickly can still be nodular melanoma.
Melanoma on Palms, Soles, and Nails
Acral lentiginous melanoma appears on the palms of the hands, soles of the feet, or under the nails. In its early stages, it looks like a light to dark brown or black flat patch that follows the natural ridges of the skin. Over time it can become nodular, develop more colors (particularly blue and black), or ulcerate.
When melanoma develops under a fingernail or toenail, it usually shows up as a brown or black streak running lengthwise through the nail. The nail itself may become distorted or damaged. One important clue is called Hutchinson’s sign: pigment that extends from under the nail out onto the surrounding skin fold. Any dark streak in a nail that is wider than 7 millimeters, contains multiple colors, or is accompanied by nail damage warrants evaluation. This subtype is more common in people with darker skin tones and is frequently diagnosed late because it occurs in areas people rarely examine.
Melanoma That Doesn’t Look Dark
About 5 percent of melanomas are amelanotic, meaning they produce little or no pigment. Instead of appearing brown or black, these melanomas show up as pink, red, or skin-colored spots. They’re easily mistaken for a pimple, scar, or other harmless skin mark. Because they lack the dark coloring most people associate with melanoma, amelanotic melanomas are often overlooked and tend to be diagnosed at a more advanced stage.
If you have a pink or reddish spot that persists for weeks, doesn’t heal, or slowly grows, it’s worth having a dermatologist look at it, even if it doesn’t match the classic image of a dark, irregular mole.
How Melanoma Differs From Common Look-Alikes
Seborrheic keratoses are among the most common benign growths that get confused with melanoma. They tend to be flat or slightly raised, waxy in texture, and painless. They often look like they’ve been stuck onto the skin’s surface and have a consistent, well-defined border. Melanoma, by contrast, tends to have irregular or blurred edges, uneven coloring, and changes over time.
Atypical moles (also called dysplastic nevi) sit in a gray zone. They can share several features with melanoma: irregular shape, blurry or ragged edges, a mix of colors including pink, red, tan, brown, and black, and a size larger than a pencil eraser. The key difference is behavior. An atypical mole that has looked the same for years is far less concerning than one that’s actively changing in size, shape, or color. People with many atypical moles do carry a higher lifetime risk of melanoma, which makes regular skin checks especially important.
What Change Looks Like in Practice
The “E” in the ABCDE rule, evolving, may be the single most useful warning sign. A mole that was once flat and is now raised. A spot that was uniformly brown and now has a darker patch or a new shade of blue. A growth that has started itching, bleeding, or crusting when it never did before. Any of these shifts over weeks or months signals that something is actively happening in the skin.
Taking photos of moles you want to monitor gives you a reliable baseline. It’s surprisingly hard to remember exactly how a mole looked three months ago, and side-by-side comparison makes subtle changes much easier to spot. Monthly self-exams that include the scalp, between the toes, the soles of the feet, and the backs of the ears cover the areas most people skip. Men over 50 face an elevated risk of melanoma compared to the general population, making routine checks particularly valuable for that group.