A cancerous mole typically looks different from your other moles in at least one noticeable way: it may be lopsided, have uneven edges, contain multiple colors, or change over time. But skin cancer doesn’t always look like a dark, irregular mole. It can also appear as a pearly bump, a scaly patch, a pink nodule, or even a dark streak under a fingernail. Knowing what to look for across all these forms gives you the best chance of catching something early.
The ABCDE Rule for Melanoma
Melanoma is the most dangerous form of skin cancer, and dermatologists use a five-letter checklist to describe its early warning signs. A mole doesn’t need all five features to be suspicious. Even one is worth getting checked.
- Asymmetry. One half of the mole doesn’t match the other. Normal moles are roughly symmetrical.
- Border. The edges are ragged, notched, or blurred rather than smooth. Pigment may spread into the surrounding skin.
- Color. Instead of one uniform shade of brown, the mole contains a mix of brown, black, tan, red, white, blue, or pink.
- Diameter. The spot is larger than 6 millimeters, roughly the size of a pencil eraser. Melanomas can be smaller, but most exceed this threshold.
- Evolving. The mole has changed in size, shape, color, or texture over the past few weeks or months, or it has started bleeding or itching.
The Ugly Duckling Sign
Sometimes the easiest way to spot a problem isn’t analyzing a single mole. It’s noticing which mole doesn’t belong. Most people’s moles share a general “family resemblance,” similar size, shape, and color. A mole that looks nothing like the rest is called an “ugly duckling,” and researchers at Harvard Health have found that this approach is just as accurate at flagging melanomas as checking each mole individually with the ABCDE criteria. It also reduces unnecessary biopsies. So if one mole on your body stands out as clearly different from all the others, that’s a reason to have it evaluated.
Atypical Moles vs. Melanoma
Not every odd-looking mole is cancer. Atypical moles (sometimes called dysplastic nevi) share some visual overlap with melanoma, which can be confusing. They tend to be flat with a slightly pebbly surface, have blurry or ragged edges, mix colors like pink, red, tan, and brown, and measure larger than a pencil eraser.
The key difference is stability. An atypical mole may look unusual, but it stays the same over months and years. Melanoma changes. It grows, shifts color, bleeds, itches, or develops new features. If you have several atypical moles, you’re at higher risk for melanoma and benefit from regular skin checks, but the moles themselves are not cancer unless they start evolving.
Nodular Melanoma: The Fast-Growing Exception
The ABCDE rule works well for the most common types of melanoma, but nodular melanoma plays by different rules. Instead of spreading outward across the skin, it grows upward and downward, forming a firm, dome-shaped bump that develops over just weeks to months. It can look like a blood blister. The texture ranges from smooth to rough and crusty, almost like cauliflower. It feels hard or firm when you press on it.
Nodular melanomas are usually larger than 1 centimeter across (about the length of a staple) and taller than 6 millimeters. Because they grow so quickly, the “evolving” part of the ABCDE rule is the most reliable flag here. Any new, firm, dome-shaped bump on your skin that appeared recently and keeps growing deserves prompt attention.
Melanoma Without Dark Pigment
One of the trickiest forms of skin cancer is amelanotic melanoma, which contains little or no dark pigment. Instead of appearing brown or black, it shows up as a pink, red, or skin-toned spot. It can be flat, slightly raised, or a firm nodule. Because it doesn’t look like what most people picture when they think of skin cancer, it’s frequently mistaken for a pimple, bug bite, or scar, and diagnoses are often delayed. If you have a pink or reddish spot that doesn’t heal within a few weeks, or that slowly grows, it’s worth having a dermatologist look at it.
Melanoma on Palms, Soles, and Nails
Acral lentiginous melanoma appears in places most people don’t think to check: the palms of the hands, soles of the feet, and under fingernails or toenails. On the palm or sole, it looks like an unevenly pigmented brown or black spot that doesn’t match the surrounding skin and grows over time. Under a nail, it typically appears as a dark streak or band of color running from the cuticle to the tip.
This type of melanoma is the most common form diagnosed in people with darker skin tones, partly because other forms of melanoma are less common in darker skin and partly because these locations are easy to overlook. Checking your nails, palms, and the bottoms of your feet during self-exams matters.
Basal Cell Carcinoma
Basal cell carcinoma is the most common skin cancer overall, and it rarely looks like a mole. On lighter skin, it often appears as a slightly translucent or pearly bump, sometimes pink, where you can almost see through the surface. Tiny blood vessels may be visible on or around it, and it may bleed and scab over repeatedly without fully healing.
On darker skin, basal cell carcinoma often looks brown or glossy black with a rolled border, which can make it harder to distinguish from a mole. Other forms include flat, scaly patches with a raised edge, or white, waxy, scar-like areas without a clear border. A lesion with dark spots and a translucent border is another variation. The common thread is a spot that doesn’t heal, slowly grows, or bleeds and crusts over again and again.
Squamous Cell Carcinoma
Squamous cell carcinoma, the second most common skin cancer, tends to look rougher and more textured than basal cell. It can appear as a firm bump on the skin that’s pink, red, brown, or black depending on your skin tone. It can also show up as a flat sore with a scaly crust, a rough scaly patch on the lip that becomes an open sore, or a wartlike raised area. A new sore developing on an old scar is another classic presentation.
Unlike melanoma, squamous cell carcinoma rarely starts as something that looks like a mole. It’s more likely to start as a rough, scaly patch or a sore that won’t heal. Sun-exposed areas like the face, ears, lips, and backs of the hands are the most common locations, but it can develop anywhere on the body.
What to Watch During Self-Checks
A monthly skin self-exam is the simplest way to catch changes early. The goal isn’t to diagnose anything yourself. It’s to notice change. Stand in front of a full-length mirror in bright light and check your entire body, including your scalp (use a handheld mirror or ask someone to help), between your toes, the soles of your feet, your palms, and under your nails.
Look for any mole that has changed size, shape, or color since your last check. Look for new spots that appeared in the past month, especially if they look different from your other moles. Look for sores that bleed, crust, and don’t fully heal. And look for firm, raised bumps that weren’t there before. Taking photos of moles you want to track makes it much easier to spot subtle changes over time.