A cancerous mole typically looks different from your other moles. It may be asymmetrical, have uneven borders, contain multiple colors, measure larger than 6 millimeters (about the size of a pencil eraser), or change noticeably over weeks to months. But melanoma doesn’t always follow that pattern. Some forms look nothing like a typical dark mole, appearing instead as a pink bump, a bruise on your foot, or a dark streak under a fingernail.
The ABCDE Features of Melanoma
The most widely used framework for spotting a suspicious mole is the ABCDE rule, developed to describe early melanoma features:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles tend to be roughly symmetrical.
- Border: The edges are ragged, notched, or blurred rather than smooth. Pigment may spread into the surrounding skin.
- Color: Multiple shades are present within the same spot. You might see brown, tan, and black mixed together, or areas of white, gray, red, pink, or blue.
- Diameter: Most melanomas are larger than 6 millimeters wide (roughly a quarter inch), though they can start smaller.
- Evolving: The mole has changed in size, shape, or color over the past few weeks or months. Any visible change in a previously stable mole is worth attention.
These features are helpful starting points, but they describe the most common presentation. Several types of melanoma break these rules entirely.
The Ugly Duckling Sign
Your moles generally resemble each other. They share a similar color palette, size range, and shape because the same genetic factors influence how your skin produces pigment spots. A melanoma often stands out simply because it looks nothing like the moles around it. Dermatologists call this the “ugly duckling” sign: the one spot on your body that doesn’t match the rest. If you have mostly small, light brown moles and one spot is dark, raised, or differently shaped, that outlier deserves a closer look, even if it doesn’t hit every ABCDE criterion.
Nodular Melanoma: The Raised, Fast-Growing Type
Not all melanomas start as flat, spreading spots. Nodular melanoma grows vertically into the skin rather than spreading outward, which makes it more dangerous and harder to catch early. It develops rapidly, often over just weeks to months, and appears as a firm, dome-shaped bump on the skin. The texture can be smooth, crusty, or rough like cauliflower. It may look like a blood blister.
Color varies widely. Nodular melanomas can be red, pink, brown, black, blue-black, or even the same color as your surrounding skin. They’re generally larger than 1 centimeter across (about the length of a staple) and raised higher than 6 millimeters. Because they can be skin-colored or red rather than dark, people often mistake them for pimples or insect bites that won’t heal.
Pink and Skin-Colored Melanomas
Amelanotic melanoma lacks the dark pigment most people associate with skin cancer. It appears as a pink or red spot on the skin, which makes it one of the easiest melanomas to miss. Without the telltale brown or black coloring, these lesions can resemble a scar, a rash, or an irritated patch of skin. If you have a pink or reddish spot that persists for weeks and doesn’t respond to typical skin care, it’s worth having a dermatologist examine it.
Melanoma on Hands, Feet, and Nails
Acral lentiginous melanoma develops in places most people forget to check: the soles of the feet, palms of the hands, and under the nails. On the palms or soles, it appears as a black or brown discoloration that can resemble a bruise or stain. Unlike a real bruise, it doesn’t fade over time. Instead, it gradually grows larger.
Under the nails, this type is called subungual melanoma. It usually shows up as a dark vertical streak running from the base of the nail to the tip, most commonly on the big toe, thumb, or index finger. The streak may start narrow, less than 3 millimeters wide, but it can widen over time to cover the entire nail and extend into the cuticle. The color is typically dark brown or black and may have irregular shading. As it progresses, it can cause the nail to crack or break. People frequently mistake it for a fungal infection or dried blood under the nail, which delays diagnosis.
Most Melanomas Appear on Normal Skin
A common assumption is that melanoma always develops from an existing mole. In reality, about 71% of melanomas arise on previously clear skin, according to a meta-analysis of 38 studies published in the Journal of the American Academy of Dermatology. Only about 29% develop from a pre-existing mole. This means you need to watch for entirely new spots on your body, not just changes in moles you already have. A spot that wasn’t there a few months ago and looks different from your other marks deserves the same scrutiny as a changing mole.
What Color Changes Mean
Color is one of the most reliable visual clues. A normal mole is usually a single uniform shade of brown. A melanoma often contains a patchwork of colors within the same lesion: tan, brown, black, and sometimes blue, gray, red, pink, or white areas. White or gray patches within a dark mole can signal regression, where the body’s immune system is attacking part of the tumor. Regressing areas may look like scar tissue or show a “peppered” blue-gray pattern. While regression sounds like a good thing, it can make the melanoma harder to measure accurately and doesn’t mean it’s gone.
How to Check Your Own Skin
A monthly self-exam is the standard recommendation. The best time is right after a shower, when your skin is fully visible and you’re already undressed. You’ll need a well-lit room, a full-length mirror, and a handheld mirror for hard-to-see areas. Having a partner help with your back and scalp makes a significant difference.
Work systematically from head to toe. Start with your face, ears, and neck in the mirror, then move to your chest, belly, and underarms. Check both sides of your arms, the tops and palms of your hands, between your fingers, and under every fingernail. Sit down to examine the fronts of your thighs, shins, tops of your feet, between your toes, and under your toenails. Use the handheld mirror for the bottoms of your feet, calves, backs of your thighs, buttocks, genital area, and your entire back. Part your hair with a comb or blow dryer to examine your scalp.
What you’re looking for is anything new, anything changing, and anything that looks different from the spots around it. Taking phone photos of moles you want to track makes it easier to notice subtle shifts from month to month.