A cancerous mole typically looks different from your other moles in at least one obvious way: it’s asymmetrical, has irregular borders, contains multiple colors, is larger than 6 millimeters (about the size of a pencil eraser), or has changed recently. Any one of these features is worth getting checked. But not every suspicious-looking mole turns out to be cancer, and not every skin cancer looks like what you’d expect. Here’s how to evaluate what you’re seeing on your skin.
The ABCDE Rule for Melanoma
Dermatologists use a five-part checklist to evaluate moles. It’s designed to catch melanoma, the most dangerous type of skin cancer, and it works just as well at home in front of a mirror.
- Asymmetry. If you drew a line down the middle of the mole, the two halves wouldn’t match. Normal moles are roughly symmetrical.
- Border. The edges are ragged, notched, or blurred rather than smooth and well-defined. The pigment may look like it’s bleeding into the surrounding skin.
- Color. Instead of one uniform shade of brown, you see a mix: brown, tan, black, or even patches of red, white, pink, blue, or gray within the same mole.
- Diameter. The mole is larger than 6 millimeters across, roughly the width of a pencil eraser. Melanomas can be smaller than this, but most are at least this size at diagnosis.
- Evolving. The mole has changed in size, shape, color, or texture over the past few weeks or months. New symptoms like itching or bleeding also count.
You don’t need all five features to be concerned. A mole that meets even one of these criteria, especially “evolving,” deserves a professional look.
The Ugly Duckling Test
There’s a simpler, more intuitive approach that works alongside the ABCDE rule. Most of your moles probably share a general “family resemblance,” similar size, color, and shape. The ugly duckling is the one that doesn’t fit in. It’s the dark mole among light ones, the large one among small ones, or the only mole that’s changed while the rest stayed stable. French researchers found that scanning for an ugly duckling among all your moles can be just as effective at identifying melanoma as evaluating each mole individually with formal criteria. If one mole stands out from the crowd, that’s your signal.
Skin Cancer That Doesn’t Look Like a Mole
Melanoma gets the most attention, but it’s not the only skin cancer. Squamous cell carcinoma often appears as a firm bump (pink, red, brown, or skin-colored), a flat sore with a scaly crust, or a rough patch on the lip. It can also develop as a new raised area on an old scar. The hallmark sign is a sore that won’t heal. If you have a scab or open wound that hasn’t closed in about two months, that’s a red flag.
Basal cell carcinoma, the most common skin cancer overall, frequently shows up as a pearly or waxy bump, a flat flesh-colored or brown scar-like patch, or a bleeding sore that heals and returns. These cancers grow slowly and rarely spread to other parts of the body, but they can cause significant local damage if ignored.
Skin Cancer on Darker Skin Tones
Most skin cancer images online show signs on light skin, which can make it harder for people with darker skin to recognize warning signs. One type of melanoma, called acral lentiginous melanoma, occurs equally across all races and accounts for the majority of melanoma cases in people of color. It doesn’t appear on sun-exposed areas. Instead, it shows up on the palms of the hands, the soles of the feet, or under fingernails and toenails.
On the palms or soles, it looks like a black or brown discoloration that might resemble a bruise or stain but grows over time. Under a nail, it appears as a dark vertical streak running the length of the nail bed. As it progresses, the nail may crack or break. It’s easy to mistake for a fungal infection or an old injury, so any persistent dark streak under a nail that you can’t explain warrants attention.
What Happens at the Dermatologist
A dermatologist won’t just eyeball your mole and guess. The standard first step is dermoscopy, a handheld magnifying device with a special light that reveals structures beneath the skin’s surface invisible to the naked eye. Studies show dermoscopy significantly improves the accuracy of skin cancer detection compared to a visual exam alone. It lets the dermatologist see patterns in pigmentation, blood vessel arrangement, and other features that distinguish a harmless mole from a potentially dangerous one.
If the mole looks suspicious under dermoscopy, the next step is a biopsy, removing part or all of the mole so it can be examined under a microscope. The preferred approach is usually an excisional biopsy, where a scalpel removes the entire mole along with a small margin of healthy skin. This typically requires a few stitches. For certain situations, a punch biopsy may be used instead, where a small circular blade presses into the skin to remove a deeper core sample. A pathologist then examines the tissue and determines whether cancer cells are present.
The biopsy is the only way to know for certain whether a mole is cancerous. No visual exam, no matter how skilled, replaces that lab confirmation.
Why Early Detection Matters
Melanoma caught early is one of the most treatable cancers. When it’s still confined to its original location in the skin (the localized stage), the five-year survival rate is 100%, according to data from the National Cancer Institute’s SEER program. Once it spreads to nearby lymph nodes, that number drops to 76%. If it reaches distant organs, it falls to 34%. The difference between a perfect prognosis and a serious one often comes down to timing, catching the melanoma before it has a chance to grow deeper or spread.
How to Check Your Own Skin
There’s no official consensus on exactly how often to do a self-exam, but regularly checking your skin for changes is the most practical thing you can do at home. The CDC recommends monitoring your moles consistently so you’ll notice if something shifts. A monthly check is a reasonable rhythm for most people.
Use a full-length mirror and a hand mirror to see your back, the backs of your legs, and your scalp. Check between your toes, on your soles, on your palms, and under your nails. If you have a partner, ask them to scan areas you can’t easily see. Taking photos of moles you want to track makes it much easier to spot subtle changes over time. You’re looking for anything new, anything that’s changed, and anything that looks different from the rest of your moles.
If you have a history of skin cancer, many atypical moles, or a family history of melanoma, your dermatologist will likely recommend regular professional full-body skin exams on a schedule tailored to your risk level. For people without those risk factors, staying consistent with self-checks and bringing anything concerning to a dermatologist promptly is a solid approach.