A cancerous mole typically looks different from your other moles in at least one obvious way: it’s asymmetrical, has uneven color, has jagged edges, or has changed recently. Most melanomas are larger than 6 millimeters (about the size of a pencil eraser), though roughly 28% are smaller than that at diagnosis. The key is knowing what patterns to look for, including some that don’t match the “dark mole” image most people picture.
The ABCDE Checklist
Dermatologists use five features to flag suspicious moles. Not every melanoma will have all five, but any one of them is worth getting checked.
- Asymmetry. If you drew a line through the middle, the two halves wouldn’t match. Normal moles are roughly symmetrical.
- Border irregularity. The edges are ragged, notched, or blurred rather than smooth. Pigment may spread or fade into the surrounding skin.
- Color variation. Instead of one uniform shade, you see a mix of brown, tan, and black, sometimes with patches of white, gray, red, pink, or blue within the same spot.
- Diameter. The spot is larger than 6 millimeters across, roughly the width of a pencil eraser. But this rule has limits (more on that below).
- Evolving. The mole has changed in size, shape, color, or texture over recent weeks or months. Any new symptom like itching, bleeding, or crusting also counts.
Why Small Moles Still Matter
The 6-millimeter diameter guideline is useful but far from perfect. In a study of 292 melanoma patients, 81 of them (28%) had melanomas smaller than 6 millimeters. Among those smaller melanomas, 36% had already become invasive, meaning the cancer had begun growing deeper into the skin. Some even showed signs of aggressive cell division or ulceration. Relying on size alone to decide whether a mole is concerning can delay diagnosis. A small spot that is asymmetrical, multicolored, or changing deserves the same attention as a large one.
Melanomas That Don’t Look Like Dark Moles
Not all skin cancers are dark brown or black. Amelanotic melanomas produce little to no pigment, so they can appear pink, red, or skin-colored. They often look like a small reddish bump with a smooth, shiny surface, or a flat pinkish patch. Some develop a nodule or a shallow ulcer. Because they lack the classic dark coloring people associate with melanoma, they’re easy to dismiss as a pimple, bug bite, or scar that won’t heal. Light-colored lesions with faint hints of brown, blue, or gray can also be melanoma in disguise.
How Cancerous Moles Grow and Change
Melanoma typically goes through two growth phases. In the radial phase, the cancer spreads outward across the skin’s surface, appearing as an irregularly shaped, flat patch. It may invade slightly deeper but hasn’t formed a raised lump yet. This is often the window where it’s most treatable.
In the vertical phase, the cancer starts growing downward into deeper tissue and forms a visible nodule or bump. A mole that was once flat and is now raised, or a raised mole that’s getting thicker, could be entering this more dangerous stage. Any noticeable change in height, texture, or shape over weeks to months is a red flag.
What It Looks Like on Darker Skin
Melanoma occurs across all skin tones, but it shows up in different locations depending on your background. Acral lentiginous melanoma, the most common type in people of color, appears on the palms of the hands, soles of the feet, or under the nails. On the sole or palm, it looks like a brown or black discoloration that may resemble a bruise or stain but grows in size over time.
Under a fingernail or toenail, melanoma usually starts as a dark vertical streak running from the base of the nail toward the tip. In about 65% of cases, it begins this way. Suspicious streaks tend to be wider than 3 millimeters, get wider toward the cuticle, and have irregular edges. Over time the nail may thicken, crack, split, or become painful. One important sign is pigment spreading beyond the nail itself onto the surrounding skin fold. This is called the Hutchinson sign and is a strong indicator of melanoma under the nail, though it can occasionally appear in non-cancerous conditions too. The thumb, big toe, and index finger are the most commonly affected digits.
Other Skin Cancers and How They Differ
Melanoma isn’t the only skin cancer that can develop from or near a mole-like spot. Two other common types look quite different.
Basal cell carcinoma typically appears as a pearly, flesh-colored or pinkish bump with a shiny surface. It grows very slowly and tends to develop on sun-exposed areas like the face, ears, and neck. You may notice tiny blood vessels visible on its surface, a rolled or raised border, or a central depression that sometimes ulcerates. It rarely looks like a traditional mole.
Squamous cell carcinoma often presents as a flat sore with a scaly, crusty surface, or a rough, scaly patch that won’t go away. On the lip, it may start as a persistent rough spot and progress to an open sore. A sore or scab that hasn’t healed within about two months is a hallmark sign.
How to Check Your Own Skin
The American Cancer Society recommends monthly self-exams for anyone with a family history of melanoma, and the American Academy of Dermatology encourages regular self-checks for everyone. If you have five or more unusual-looking moles or 100 or more regular moles, guidelines from several countries recommend professional skin exams every 6 to 12 months.
When you do a self-exam, check everywhere: between your toes, on the soles of your feet, under your nails, on your scalp (use a blow dryer to part your hair), and on your back with a hand mirror. The goal isn’t to diagnose anything yourself. It’s to notice change. Take photos of moles you want to track so you have a baseline to compare against. Any spot that looks different from your other moles, or different from how it looked a few months ago, is worth showing to a dermatologist.