Melanomas can look surprisingly different from one another, but most share a few telltale features: uneven color, irregular shape, and change over time. Some appear as flat, spreading patches of mixed brown and black. Others look like raised, firm bumps. A small percentage have no dark pigment at all, appearing pink or red instead. Knowing the full range of what melanoma can look like is critical, because catching it early dramatically improves outcomes.
The ABCDE Rule
The most widely used framework for spotting melanoma is the ABCDE rule, developed by the National Cancer Institute. Each letter flags a specific warning sign:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles are roughly symmetrical.
- Border irregularity: The edges are ragged, notched, or blurred rather than smooth. Pigment may bleed into the surrounding skin.
- Color variation: Instead of one uniform shade, you see a mix of brown, black, and tan, sometimes with patches of white, gray, red, pink, or blue.
- Diameter: Most melanomas are larger than 6 millimeters across (about the width of a pencil eraser), though they can be smaller when first detected.
- Evolving: The mole has changed in size, shape, or color over recent weeks or months.
Not every melanoma checks all five boxes, and not every mole that checks one box is melanoma. The “evolving” criterion is arguably the most important single factor. Any mole that is clearly changing deserves a closer look.
The 6mm Rule Has Limits
The traditional guidance says to worry about moles larger than 6 millimeters, but this threshold can be misleading. In a study of 292 patients with pigmented skin lesions, 81 had lesions 6 millimeters or smaller, and 29 of those turned out to be invasive melanoma. Dismissing a spot because it’s small can delay diagnosis. Size matters, but it’s just one piece of the puzzle. A small mole that’s asymmetric, multicolored, or changing should still be evaluated.
Superficial Spreading Melanoma
The most common subtype is superficial spreading melanoma, which accounts for the majority of cases. It typically starts as a flat or slightly raised brown patch with irregular, asymmetric borders and areas of black, blue, or pink mixed in. These lesions spread outward across the skin surface for months or even years before growing deeper into tissue. In men, they most often appear on the head, neck, and trunk. In women, the lower legs are a particularly common location.
Because they grow horizontally for a long time before becoming invasive, superficial spreading melanomas offer a wider window for early detection compared to other subtypes.
Nodular Melanoma: Raised and Fast-Growing
Nodular melanoma looks and behaves very differently. Instead of spreading outward across the skin, it grows vertically, pushing both upward as a raised bump and downward into deeper tissue. It develops quickly, often over just weeks or months. It’s firm to the touch and may resemble a blood blister. Most nodular melanomas are larger than 1 centimeter across (about the length of a staple) and taller than 6 millimeters.
This subtype is particularly dangerous because most of the cancer grows below the surface, like an iceberg. The visible bump on the skin represents only a fraction of what’s happening underneath. Some doctors use the “EFG” criteria for this type: Elevated, Firm, and Growing. If a new bump on your skin is firm, dome-shaped, and getting bigger over weeks, that’s a red flag even if it doesn’t match the classic flat, spreading melanoma image.
Melanoma on Palms, Soles, and Nails
Acral lentiginous melanoma appears on the palms of the hands, soles of the feet, or under the nails. It shows up as an unevenly pigmented black or brown spot that looks different from the surrounding skin and grows over time. This subtype is frequently mistaken for a bruise, blood blister, or wart, which delays diagnosis. People often don’t seek care until the spot starts bleeding or causes discomfort when walking.
When melanoma develops under a fingernail or toenail, it usually appears as a dark vertical streak running from the base of the nail to the tip, as if someone drew a line with a brown or black marker. The streak typically starts narrow (under 3 millimeters wide) but widens over time, especially at the base. The color may be irregular, with varying shades of blackish brown. Eventually, the streak can expand to cover the entire nail.
One important sign is when the dark pigment extends beyond the nail itself and discolors the surrounding skin at the cuticle. This is known as the Hutchinson sign, and it strongly suggests melanoma rather than a benign cause of nail discoloration.
Melanoma on Sun-Damaged Skin
Lentigo maligna is a slow-growing form that develops on chronically sun-damaged skin, most often on the face, ears, or neck of older adults. It creates a blotchy appearance with uneven pigmentation, and its borders are often hard to define clearly. Because it blends into the mottled, sun-damaged skin around it, lentigo maligna can be easy to overlook or dismiss as an age spot.
Melanomas That Aren’t Dark
About 5 percent of melanomas are amelanotic, meaning they lack the dark pigment most people associate with skin cancer. These appear as pink or red spots on the skin rather than brown or black ones. Because they don’t match the typical mental image of melanoma, amelanotic melanomas are frequently overlooked or mistaken for harmless skin conditions. As a result, they tend to be diagnosed at a later stage than pigmented melanomas.
This is an important reason not to rely on color alone when evaluating a suspicious spot. A pink, skin-toned, or reddish lesion that is firm, growing, or otherwise unusual still warrants attention.
What to Actually Watch For
The single most practical thing you can do is pay attention to change. A mole that has looked the same for years is far less concerning than one that is new, growing, shifting in color, or developing irregular borders. The “ugly duckling” approach is also useful: look for the mole that doesn’t look like your other moles. Most people’s moles share a family resemblance with one another. The outlier, the one that looks distinctly different from the rest, is worth having checked.
Melanoma can appear anywhere on the body, including places you might not think to check: between the toes, on the soles of the feet, under nails, on the scalp, and even inside the mouth. Regular self-exams that include these hidden areas make a real difference in how early melanoma gets caught.