Melanoma has a distinct set of visual warning signs you can check at home, and catching it early dramatically improves outcomes. The most widely used method is the ABCDE rule, which gives you five specific features to look for in any mole or spot on your skin. But some melanomas break the rules, appearing pink, dome-shaped, or hidden under a toenail. Knowing what to look for, including the exceptions, is what makes self-screening effective.
The ABCDE Rule
Dermatologists and cancer organizations consistently point to five features that distinguish melanoma from ordinary moles. You can evaluate any spot on your body using these criteria:
- Asymmetry. One half of the spot doesn’t match the other. A normal mole is roughly symmetrical. If you drew a line down the center and the two halves look noticeably different, that’s a flag.
- Border irregularity. The edges are ragged, notched, scalloped, or blurred rather than smooth and well-defined. Pigment may appear to spread or fade into the surrounding skin.
- Color variation. Instead of one uniform shade, the spot contains a mix of colors: tan, brown, black, or unexpected shades like white, gray, red, pink, or blue. Multiple colors within a single lesion are more suspicious than a uniformly dark mole.
- Diameter. Most melanomas are larger than 6 millimeters when diagnosed, roughly the size of a pencil eraser. That said, melanomas can be smaller, so size alone shouldn’t reassure you.
- Evolving. Any change in size, shape, color, or texture over weeks or months is the single most important warning sign. A mole that looked the same for years and suddenly starts changing deserves attention.
Not every melanoma hits all five criteria. Some early melanomas check only one or two boxes. The “E” criterion, a spot that’s actively changing, is often the one that catches melanomas the ABCD features miss.
The Ugly Duckling Sign
The ABCDE rule evaluates one spot in isolation. The ugly duckling sign takes a different approach: it compares a spot to all the other moles on your body. Most people’s moles share a family resemblance. They tend to be similar in size, shape, and color. A mole that looks nothing like its neighbors, the “outlier,” is the one most likely to be malignant.
This method is especially useful if you have many moles, because it helps you focus on the one that doesn’t belong rather than evaluating dozens individually. Research in dermatology journals has found that the ABCDE rule and the ugly duckling sign are complementary. Neither one catches everything the other does, so using both together gives you the best chance of spotting something early.
Nodular Melanoma: The Fast-Growing Exception
Not all melanomas spread outward in a flat, irregular patch. Nodular melanoma grows vertically, pushing up from the skin surface rather than spreading sideways. It accounts for a significant portion of thick, dangerous melanomas because it can develop quickly and doesn’t always follow the ABCDE pattern. These lesions may be symmetrical, have smooth borders, and appear as a single uniform color.
For nodular melanoma, look for the EFG features instead:
- Elevated. The spot is raised above the skin surface, not flat.
- Firm. It feels hard or solid to the touch, unlike the soft texture of most benign moles.
- Growing. It’s changing noticeably over days to weeks, not months.
A new bump on your skin that is firm, raised, and growing rapidly, even if it looks nothing like a “typical” melanoma, is worth having examined promptly.
When Melanoma Doesn’t Look Dark
Amelanotic melanoma is the variant most likely to be missed because it lacks the dark pigment people associate with skin cancer. These lesions can appear pink, red, skin-colored, or only faintly tan. About half still contain small traces of residual pigment, but it may not be obvious to the naked eye.
Because these melanomas don’t trigger the usual “dark and irregular” alarm, they’re often mistaken for pimples, bug bites, or scar tissue. The clue is persistence: a pink or reddish spot that doesn’t heal, slowly grows, or feels firm and raised warrants a closer look. The vast majority of amelanotic melanomas (over 80% in one study) are invasive by the time they’re diagnosed, which reflects how easily they’re overlooked.
Melanoma on Hands, Feet, and Nails
Acral lentiginous melanoma appears on the palms, soles of the feet, and under fingernails or toenails. It’s the most common type of melanoma in people with darker skin tones. These lesions are frequently misdiagnosed as fungal infections, warts, or diabetic foot ulcers, which delays treatment.
On the soles or palms, look for an irregularly pigmented patch with multiple shades of brown, black, and gray arranged asymmetrically. Under a nail, the hallmark is a dark longitudinal streak, a brown or black line running the length of the nail. About two-thirds of nail melanomas present with this streak, though nail trauma and fungal infections can look similar.
A key red flag for nail melanoma is the Hutchinson sign: pigment that extends beyond the nail onto the surrounding skin of the cuticle or fingertip. Other concerning features include a streak affecting the first finger or toe, pigmentation covering more than two-thirds of the nail plate, and black or gray coloring with irregular line width. The CUBED acronym was developed specifically for spotting melanoma on the feet and under nails: a Colored lesion, Uncertain diagnosis, Bleeding, Enlargement, or Delay in healing.
How to Do a Monthly Skin Check
A thorough self-exam takes about 10 minutes once you’ve done it a few times. Check your skin about once a month, ideally after a bath or shower when your skin is clean and you’re already undressed. You need a well-lit room, a full-length mirror, and a hand-held mirror.
Start by facing the full-length mirror and scanning your entire front, then turn and examine your back. Raise your arms and check both sides of your torso. Use the hand mirror to see the back of your neck and scalp, parting your hair section by section (a blow dryer can help move hair out of the way). Check under your breasts if applicable. Sit down to examine your legs, the soles of your feet, and between your toes. Bend your elbows and inspect your forearms, upper arms, palms, and between your fingers. Don’t skip the inside of your mouth: check your lips, tongue, and inner cheeks.
Taking photos of moles you’re monitoring makes it much easier to notice change over time. Your phone camera is fine for this. Compare photos month to month and look for any shift in size, shape, color, or texture.
What Happens if a Spot Looks Suspicious
A dermatologist’s first tool is dermoscopy, a handheld device with magnification and polarized light that reveals structures invisible to the naked eye. Under dermoscopy, melanomas show patterns like irregular pigment networks, blue-white veils, and abnormal blood vessel arrangements. On the soles of the feet, melanoma displays a characteristic pattern where pigment follows the ridges of the skin rather than the furrows, which is the opposite of what benign moles do.
If a lesion looks concerning under dermoscopy, the next step is a biopsy. The type of biopsy matters. An excisional biopsy, which removes the entire spot, provides the most accurate diagnosis. Only 2% of patients who had an excisional biopsy needed their treatment plan changed after later surgery, compared to 18% of those who had a punch biopsy (a smaller, partial sample). Punch biopsies missed residual melanoma 69% of the time, and they were far more likely to result in an incorrect initial staging of the cancer. If your doctor recommends a biopsy, it’s reasonable to ask whether a full excision is appropriate for your situation.
AI Skin-Checking Apps
Smartphone apps that use artificial intelligence to analyze photos of moles have improved considerably. A recent meta-analysis found that AI systems detect melanoma with a sensitivity of 86%, meaning they correctly flag about 86 out of 100 melanomas. Specificity was 94%, meaning they correctly identify most benign spots as harmless. Those numbers are comparable to general practitioners, though still below experienced dermatologists for complex cases.
These apps can be a useful screening layer, especially if you have many moles and want help prioritizing which ones to show a doctor. They should not replace professional evaluation. A 14% miss rate means roughly 1 in 7 melanomas could be overlooked, and apps perform worst on the variants that are already hardest to spot: amelanotic lesions, nodular melanoma, and acral melanoma on darker skin.