Melanoma typically appears as an unusual mole or spot with uneven color, irregular edges, and an asymmetric shape. It can be brown, black, tan, red, pink, or even skin-colored, and most are larger than 6 millimeters across (roughly the size of a pencil eraser). But melanoma doesn’t always follow the textbook description, which is why knowing the full range of appearances matters.
The ABCDE Rule for Spotting Melanoma
The most widely used framework for identifying melanoma early is the ABCDE rule, developed by the National Cancer Institute. Each letter describes a feature to look for:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles tend to be roughly symmetrical.
- Border irregularity: The edges are ragged, notched, or blurred rather than smooth and well-defined. Pigment may spread into the surrounding skin.
- Color variation: Instead of one uniform shade, you see a mix of brown, black, and tan. Some melanomas also contain areas of white, gray, red, pink, or blue.
- Diameter: The spot is larger than 6 millimeters, about the width of a pencil eraser. That said, melanomas can be smaller than this, especially early on.
- Evolution: The mole has changed in size, shape, or color over the past few weeks or months. This is often the single most important warning sign.
A mole doesn’t need to check every box to be suspicious. Even one of these features, especially evolution, is worth getting examined.
The “Ugly Duckling” Sign
If you have many moles, another useful approach is comparison. Most of your moles probably look similar to each other. A mole that stands out as clearly different from all the others, either in color, shape, size, or texture, is called an “ugly duckling.” This contrast alone can flag a melanoma that might not obviously meet the ABCDE criteria on its own. When you’re doing a skin check, step back and look for the outlier.
Melanoma That Doesn’t Look Like a Mole
Not all melanomas are flat, dark spots. Nodular melanoma grows as a firm, dome-shaped bump on the skin that’s usually hard to the touch. It develops fast, often over just a few weeks, and it may not display the classic ABCDE features. Instead, dermatologists use the EFG rule for this type: elevated, firm, and growing. Nodular melanoma can be dark brown, black, red, or pink, and it sometimes bleeds or crusts over. Because it grows so quickly, some types can become life-threatening in as little as six weeks.
Then there’s amelanotic melanoma, which produces little or no pigment. It shows up as a pink or red spot on the skin, sometimes resembling a pimple, scar, or minor irritation. Because it lacks the dark coloring people associate with melanoma, it’s frequently overlooked or mistaken for something harmless. This means it’s often diagnosed at a later, more advanced stage compared to darker melanomas.
Melanoma Under Nails
Melanoma can develop beneath a fingernail or toenail, where it typically appears as a dark vertical line running from the base of the nail to the tip. The line is usually brown or black and can easily be mistaken for a bruise. One key difference: a bruise grows out with the nail over time, while a melanoma streak stays in place or gets wider.
The discoloration may be irregular, with varying shades of blackish brown, and the band is often less than 3 millimeters wide at first but can widen. If dark pigment spreads into the skin around the nail (the cuticle or nail fold), that’s a particularly concerning sign known in clinical settings as Hutchinson’s sign.
Melanoma on Darker Skin
Melanoma in people with darker skin tones often appears in places that get little or no sun exposure. The most common locations include the palms, soles of the feet, fingers and toes, under and around nails, inside the mouth or on the lips, and the genital or anal area. A growing dark spot on your palm or sole, especially one with uneven color, is a warning sign worth taking seriously.
Specific things to look for include a dark line or streak in a nail that doesn’t grow out over time, a darker discoloration on the lip or inside the mouth, a growing bump with more than one color that may break open or bleed, and darkening skin around a nail. Because melanoma is often associated only with sun-exposed skin, it’s frequently diagnosed later in people of color, making awareness of these less typical locations especially important.
Melanoma in the Eyes and Mouth
Melanoma doesn’t only affect skin. It can develop in the eye, where it may appear as a growing dark spot on the iris (the colored part). Other signs of eye melanoma include flashes of light, floating specks in your vision, a change in pupil shape, blurry vision in one eye, or loss of side vision. Some eye melanomas produce no symptoms at all and are only found during a routine eye exam.
Mucosal melanoma can also develop on the lining of the mouth, nose, throat, or genital tract. In the mouth, it often looks like a dark, flat, or slightly raised patch that grows over time. These internal melanomas are rare, but they tend to be diagnosed later because they’re hidden from view.
How Fast Changes Happen
The speed of change varies widely. Superficial spreading melanoma, the most common type, may evolve gradually over months or even a year or two before it begins to invade deeper tissue. Nodular melanoma is the opposite extreme, growing noticeably in just weeks. Any new spot that appears and changes rapidly, or any existing mole that shifts in color, shape, or size over a period of weeks to months, deserves prompt evaluation. The “evolving” part of the ABCDE rule is the one that catches many melanomas that don’t fit neatly into the other categories.