Most moles are harmless, but a mole that is asymmetrical, has irregular borders, contains multiple colors, is larger than 6 millimeters (about the size of a pencil eraser), or has changed recently could be a sign of melanoma. These five features form the ABCDE rule, which is the most widely used framework for spotting a potentially cancerous mole. Catching melanoma while it’s still confined to the skin gives you a five-year survival rate above 99%, so knowing what to look for matters.
The ABCDE Rule
The National Cancer Institute breaks suspicious moles into five features. You don’t need all five to be present for a mole to warrant attention. Even one is enough to get it checked.
- Asymmetry: If you drew a line through the middle, the two halves wouldn’t match in shape.
- Border: The edges are ragged, notched, or blurred rather than smooth and well-defined. The pigment may bleed out into the surrounding skin.
- Color: Instead of one uniform shade of brown, you see a mix of brown, tan, black, or even patches of white, gray, red, pink, or blue within the same mole.
- Diameter: The mole is wider than 6 millimeters, roughly the width of a pencil eraser. Melanomas can be smaller than this, but most are at least this size when diagnosed.
- Evolving: The mole has visibly changed in the past few weeks or months in size, shape, color, or texture, or it has started itching, bleeding, or crusting.
Evolution is often the most important of the five. A mole that looked the same for years and suddenly starts changing deserves prompt attention, even if it doesn’t check any other boxes.
Melanomas That Don’t Look Like Typical Moles
Not every melanoma is a dark, irregular mole. Between 2% and 8% of all melanomas have little or no pigment. These are called amelanotic or hypomelanotic melanomas, and they can look like a small pink or red bump, an erythematous (reddish) plaque, or even a blister-like spot. Because they lack the classic dark coloring people associate with skin cancer, they’re easy to dismiss as a pimple, bug bite, or irritation.
Partially pigmented melanomas may show only faint light brown, light blue, or light gray coloring across part of the lesion, with the rest appearing skin-toned or pink. The key warning sign with these lighter lesions is the same as with darker ones: change over time. A pink spot that persists for weeks, grows, or develops visible blood vessels on its surface is worth having a dermatologist evaluate.
Places You Might Not Think to Check
Melanoma can develop in places that rarely see the sun. Acral lentiginous melanoma appears on the palms of the hands, the soles of the feet, or under fingernails and toenails. On the palms or soles, it often starts as a dark brown or black discoloration that resembles a bruise or stain but grows in size over time rather than fading.
Under a nail, this type of melanoma typically shows up as a dark vertical streak running the length of the nail bed. It’s sometimes mistaken for a fungal infection or a blood blister from an injury. As it progresses, it can cause the nail to crack or break. If you notice a dark streak under a nail that you can’t explain with a recent injury, and it doesn’t grow out with the nail over several months, have it examined.
Dysplastic Nevi: Moles That Look Unusual but Aren’t Cancer
Some people have moles that look suspicious under the ABCDE criteria but are actually dysplastic nevi, sometimes called atypical moles. These are typically larger than 5 millimeters, have a mix of colors from pink to dark brown, and often have irregular edges that fade into surrounding skin. Their surface tends to be flat with a slightly scaly or pebbly texture.
Dysplastic nevi are not melanoma, but they signal higher risk. Someone with more than five dysplastic nevi has roughly 10 times the melanoma risk of someone with none. If you’ve been told you have atypical moles, regular skin checks become especially important. The goal isn’t to panic about every odd-looking mole but to establish a baseline so you and your dermatologist can spot changes quickly.
Other Skin Cancers That Don’t Start as Moles
Melanoma gets the most attention, but basal cell and squamous cell carcinomas are far more common. They don’t typically arise from existing moles, and they look different.
Basal cell carcinoma often appears as a small, pink or red, shiny bump with a pearly or translucent quality. It can also show up as a flat, pale or yellowish area that looks like a scar, or as a growth with raised edges and a depressed center with visible blood vessels. These tumors are fragile and tend to bleed easily after minor bumps or shaving.
Squamous cell carcinoma commonly presents as a rough, scaly red patch that may crust or bleed, a raised lump (sometimes with a depression in the center), or a wart-like growth. Both types share one telltale sign: a sore that doesn’t heal after several weeks, or one that heals and then comes back. Any non-healing sore on sun-exposed skin should be evaluated.
How to Do a Full-Body Skin Check
The American Academy of Dermatology recommends a systematic approach so you don’t miss anything. You’ll need a full-length mirror, a hand mirror, and good lighting.
Start by standing in front of the full-length mirror. Examine your body from the front and back, then raise your arms and check both sides. Bend your elbows and look carefully at your forearms, upper arms, underarms, fingernails, and palms. Next, sit down and inspect the fronts and backs of your legs, the tops and soles of your feet, between each toe, and your toenails. Use the hand mirror to check the back of your neck, your ears, and your scalp, parting your hair in sections for a closer look. Finally, use the hand mirror to examine your back and buttocks.
The point of regular self-checks isn’t to diagnose anything yourself. It’s to notice change. Doing a check once a month creates a mental map of your skin so that a new spot or a growing mole stands out. Taking photos of moles you want to track can make it easier to compare over time.
What Happens If You Find Something Suspicious
A dermatologist will first examine the spot visually, often using a dermatoscope, a handheld magnifying device with polarized light that reveals structures beneath the skin’s surface. If the lesion looks concerning, the next step is a biopsy, which means removing a small tissue sample for examination under a microscope.
For a spot suspected to be melanoma, dermatologists generally prefer an excisional biopsy, where the entire lesion is removed along with a small margin of normal skin. This is important because the thickness of a melanoma (measured in millimeters from the surface down) determines its stage and guides treatment. Shaving off just the top could miss critical depth information. For larger lesions or spots in tricky locations, a punch biopsy, which takes a small cylindrical core of full-thickness skin, may be used instead.
Results typically come back within one to two weeks. If the biopsy confirms melanoma, the thickness measurement and whether the cancer has spread beyond the original site determine what happens next.
Why Early Detection Changes Everything
Melanoma survival depends heavily on how far the cancer has progressed at diagnosis. When melanoma is localized, meaning it hasn’t spread beyond the original site in the skin, the five-year survival rate is above 99%. Once it spreads to nearby lymph nodes (regional stage), that drops to 76%. If it reaches distant organs, the rate falls to 35%. The combined five-year survival across all stages is 95%, which reflects the fact that most melanomas are caught early.
These numbers make a strong case for paying attention to your skin. The difference between a localized melanoma and one that has spread is often just a matter of months. A monthly self-check takes about 10 minutes and puts you in the best position to catch something early, when treatment is simplest and outcomes are best.