The most reliable way to tell if a mole might be skin cancer is to look for five specific warning signs, known as the ABCDE rule, and to watch for any mole that looks noticeably different from your others. No self-check replaces a biopsy, but knowing what to look for can help you catch a suspicious spot early, when the five-year survival rate for melanoma is nearly 98%.
The ABCDE Rule
Dermatologists use five visual features to flag moles that need a closer look. You can apply these during a self-check at home:
- Asymmetry. One half of the mole doesn’t mirror the other. Normal moles tend to be roughly symmetrical.
- Border. The edges are ragged, notched, or blurred rather than smooth. The pigment may appear to bleed into surrounding skin.
- Color. Instead of a single uniform shade, the mole contains a mix of brown, black, tan, white, gray, red, pink, or blue.
- Diameter. The spot is larger than about 6 millimeters, roughly the size of a pencil eraser. That said, melanomas can be smaller. Research shows that small melanomas can be just as aggressive as large ones, so size alone isn’t a reliable way to rule anything out.
- Evolving. The mole has changed in size, shape, color, or texture over the past weeks or months. This is often considered the single most important factor. Adults over 40 generally shouldn’t be developing new moles, and existing ones shouldn’t be growing.
The Ugly Duckling Sign
The ABCDE rule evaluates one mole at a time. The ugly duckling sign takes a different approach: you compare all your moles to each other. If one stands out from the rest, it deserves attention. That could mean a single large, dark mole surrounded by smaller, lighter ones, or a small, pale mole in a cluster of darker ones. The key is that it doesn’t fit the pattern of your other spots.
This method catches melanomas that might not trigger every ABCDE criterion on their own but still look “off” relative to your baseline.
Changes That Should Prompt a Visit
Beyond the visual checklist, certain changes signal that something may be wrong. A mole that bleeds spontaneously, without being scratched or bumped, is a red flag. So is a spot that becomes persistently itchy, tender, or painful. Crusting, oozing, or a sore that won’t heal also warrant attention.
Speed matters for context. Concerning mole changes typically unfold over weeks to months. Aggressive melanomas have been reported to double in size in as little as 30 days, while basal cell carcinomas grow slowly over months to years. A mole that looks different from how it looked a few weeks ago is more urgent than one that’s been stable for a decade.
How Melanoma Looks Different From Other Skin Cancers
Not all skin cancer looks like a suspicious mole. The three most common types have distinct appearances.
Melanoma usually appears as a brown or black spot with irregular borders and uneven color. Some melanomas, though, are pink, tan, or even white. They often spread outward across the skin’s surface as they grow, so you may notice a dark spot gradually changing shape or getting bigger.
Basal cell carcinoma is the most common skin cancer and tends to show up on sun-exposed areas like the face, ears, and neck. It often looks like a shiny, pearly, or translucent bump that may be pale, pink, or red. These growths are fragile and bleed easily. Larger ones can develop oozing or crusted areas, and some have a depressed center. On darker skin, basal cell carcinomas may appear lighter or darker than the surrounding skin tone.
Squamous cell carcinoma typically presents as a flat, reddish or brownish patch with a rough, scaly, or crusted surface. It can also appear as a firm bump or a sore that heals and reopens. Some look like warts. In rare cases, squamous cell carcinoma develops under or around a nail, appearing as a discolored area that affects nail growth.
Spots You Might Not Think to Check
Most people associate skin cancer with sun-exposed areas, but melanoma can develop in places that rarely see sunlight. A type called acral lentiginous melanoma appears on the soles of the feet, palms of the hands, and under fingernails or toenails. It’s the most common form of melanoma in people with darker skin.
On the palms or soles, it starts as a black or brown discoloration that may look like a bruise or stain. Over time, it grows. Under the nails, it usually appears as a dark vertical streak running the length of the nail bed. As it progresses, it can cause the nail to crack or break. This type is often mistaken for a bruise, a fungal infection, or dried blood, which delays diagnosis.
Who Faces Higher Risk
Your natural skin tone influences your baseline risk. People with very fair skin that always burns and never tans (skin types 1 and 2 on the Fitzpatrick scale) face the highest risk and should be especially diligent about skin checks. Those with medium-toned skin that sometimes burns can still develop skin cancer from cumulative UV damage. People with deeply pigmented skin rarely burn but are not immune. When skin cancer does occur in darker-skinned individuals, it’s more likely to appear in less obvious locations like the palms, soles, and nails.
Other risk factors include a history of blistering sunburns, a large number of moles (50 or more), a family history of melanoma, and a weakened immune system.
What Happens During a Professional Check
When you bring a suspicious mole to a dermatologist, they’ll typically examine it with a dermatoscope, a handheld magnifying device with a built-in light. Dermoscopy improves detection accuracy significantly. At a comparable level of specificity, dermoscopy catches about 92% of melanomas compared to 76% with the naked eye alone.
If a spot looks suspicious under magnification, the next step is a biopsy. A shave biopsy removes a thin surface layer of skin with a razor blade and doesn’t require stitches. A punch biopsy uses a small circular tool to remove a deeper core of tissue and may need a stitch or two. Your doctor chooses the method based on the size, location, and depth of the spot. The sample goes to a lab, and results typically come back within a week or two.
Why Early Detection Matters
Melanoma caught early is highly treatable. When it’s still confined to the skin (localized), the five-year survival rate is 97.6%. Once it spreads to nearby lymph nodes (regional), that drops to 60.3%. If it reaches distant organs, the rate falls to 16.2%. The difference between catching a melanoma at its earliest stage versus its latest is enormous, and it often comes down to whether someone noticed a changing spot and acted on it.
Getting familiar with your own skin is the most practical thing you can do. Pick a regular interval, monthly works well, and look over your entire body in good lighting. Use a mirror or a partner for your back and scalp. Take photos of moles you want to track so you have a baseline for comparison. If anything changes, looks unusual, or matches the warning signs above, get it checked.