Melanoma typically appears as an unusual mole or spot on the skin with uneven color, irregular borders, and an asymmetric shape. Most are wider than 6 millimeters (about the size of a pencil eraser), though smaller ones do occur. The tricky part is that melanoma doesn’t always look the same. It can be dark brown, multicolored, pink, or even skin-toned, depending on the type.
The ABCDE Rule
The most widely used framework for spotting melanoma is the ABCDE rule, developed to describe features of early-stage disease. Each letter flags a visual warning sign:
- Asymmetry: One half of the mole doesn’t mirror the other. Normal moles tend to be roughly symmetrical.
- Border irregularity: The edges are ragged, notched, or blurred rather than smooth. Pigment may spread into the surrounding skin.
- Color variation: Instead of one uniform shade, the spot contains a mix of brown, tan, black, or even patches of white, gray, red, pink, or blue.
- Diameter: Most melanomas are larger than 6 millimeters wide, though 3 to 14 percent of all melanomas are smaller than that threshold. Size alone isn’t diagnostic, but growth matters.
- Evolving: The mole has changed in size, shape, or color over the past few weeks or months. Any noticeable change in a mole deserves attention.
No single criterion is enough on its own. A mole might be slightly asymmetric and still be perfectly benign. The ABCDE rule works best when you’re looking at all five features together.
How Melanoma Differs From a Normal Mole
A common (benign) mole is usually smaller than 6 millimeters, one even color, round or oval, and stays the same over time. A dysplastic nevus, sometimes called an atypical mole, sits somewhere in between. It’s often more than 5 millimeters wide and can have a mixture of colors from pink to dark brown, but it tends to be flat with a smooth or slightly pebbly surface. Its edges may fade into the surrounding skin, which can make it look worrying.
Melanoma shares some of those traits but pushes further. The color mix is more dramatic, with possible shades of blue, gray, or white alongside the browns and blacks. The borders are more chaotic. And critically, melanoma changes. A dysplastic nevus may look a little odd but stay stable for years. Melanoma keeps evolving.
One useful concept is the “ugly duckling” sign. Rather than analyzing a single mole in isolation, you compare it to the moles around it. Most people’s moles share a general family resemblance. If one spot looks clearly different from all the others, that outlier deserves a closer look, even if it doesn’t tick every ABCDE box.
The Most Common Type: Superficial Spreading Melanoma
About 70 percent of all melanomas are the superficial spreading type. These appear as flat or slightly raised brown patches with areas of black, blue, or pink discoloration. They’re typically wider than 6 millimeters with irregular, asymmetric borders. What distinguishes this type is its growth pattern: it spreads horizontally across the skin surface for years before growing deeper. That prolonged surface phase is actually a window of opportunity, because it’s easier to spot and treat while it’s still flat.
Nodular Melanoma: Fast and Raised
Nodular melanoma behaves differently. Instead of spreading outward slowly, it grows vertically into the skin over weeks or months. It appears as a firm, dome-shaped bump that’s hard to the touch. It can be dark brown, black, or blue-black, and it sometimes resembles a blood blister. Because it grows so quickly and doesn’t go through a long flat phase, nodular melanoma is often diagnosed later and at a more advanced stage. The ABCDE rule can miss it, since it may look symmetric and have even borders. If you notice a new, firm, rapidly growing bump on your skin, the speed of growth itself is the red flag.
Melanoma That Doesn’t Look Dark
Not all melanomas are dark. Amelanotic melanoma lacks the pigment most people associate with skin cancer. It’s usually pink or light brown and can look like an irritated patch of skin, a pimple, or a sore. Because it doesn’t match the classic image of a dark, irregular mole, it’s frequently mistaken for something harmless. It’s still somewhat distinct from the surrounding skin, but you have to look carefully. This is a rare subtype, but it’s an important reminder that melanoma isn’t always dark.
Melanoma Under Nails and on Palms or Soles
Acral lentiginous melanoma develops on the palms, soles of the feet, or under the nails. Under a nail, it first appears as a brown or black streak running lengthwise (longitudinal melanonychia). A key warning sign is called the Hutchinson sign: pigment that extends from under the nail onto the surrounding skin of the cuticle or nail fold. In studies of subungual melanoma, this sign was present in about 83 percent of cases.
Not every dark nail streak is melanoma. Benign streaks can create a look-alike called pseudo-Hutchinson sign, where pigment appears to extend through the transparent nail fold but isn’t actually in the skin itself. The concerning version tends to extend beyond half the nail width, may be wider than the streak underneath, and often shows discontinuous patches of pigment. Benign streaks are more likely to have a clean linear border and fade out toward the base of the nail.
This type of melanoma is more common in people with darker skin tones and often goes unnoticed because people don’t think to check their feet or nails for skin cancer.
Texture Changes and Physical Symptoms
Melanoma isn’t only about color and shape. As it advances, the texture of the skin can change noticeably. The surface may become hard or lumpy. It can break down and look scraped, or it may ooze and bleed. Some melanomas develop a crust. A sore that won’t heal, or that heals and comes back, is another form melanoma can take. In some cases, a slowly growing patch of thick skin that resembles a scar can actually be melanoma.
Melanoma can also cause physical discomfort: itching, tenderness, or pain. These sensations alone don’t confirm melanoma (plenty of benign conditions itch), but when a mole that previously caused no symptoms starts itching or bleeding, that change is meaningful.
Color Clues Inside the Lesion
Certain color patterns within a mole carry specific significance. White patches inside a previously pigmented mole can indicate regression, where the body’s immune system has attacked part of the melanoma. This sounds like a good thing, but irregular white areas within a lesion are actually a warning sign, occurring in roughly half of melanomas. They look different from the uniform ring of lightening you’d see in a benign halo nevus (where a pale circle forms evenly around a mole before it fades).
A blue-gray haze over part of the lesion, sometimes called a blue-white veil, is another concerning feature. It looks like a slightly blurred or frosted area within the spot, caused by thickened skin sitting over dense pigment deeper in the layers below. This feature appears in both flat and nodular melanomas.
What to Look For in Practice
Checking your skin doesn’t require memorizing every subtype. The core principle is simple: look for change, look for outliers, and look for spots that don’t behave like the rest. A mole that’s been the same for 20 years is far less concerning than one that appeared three months ago and has already shifted in color or size. A spot that looks nothing like your other moles, even if it seems small or pale, is worth having examined.
Pay attention to areas you might not think to check: the soles of your feet, between your toes, under your nails, and your scalp. Use a mirror or ask someone to look at your back. Melanoma can develop anywhere on the body, including places that rarely see sunlight.