Skin cancer often announces itself through visible changes you can spot on your own, long before it causes pain or other symptoms. The three most common types, basal cell carcinoma, squamous cell carcinoma, and melanoma, each look different on the skin. Knowing what to watch for gives you a real advantage: melanoma caught early, before it spreads, has a five-year survival rate of nearly 98%, compared to just 16% when detected at an advanced stage.
The ABCDE Rule for Melanoma
Melanoma is the most dangerous form of skin cancer, with an estimated 112,000 new cases expected in the U.S. in 2026 alone. The standard method for spotting a suspicious mole uses five visual features, abbreviated as ABCDE.
Asymmetry means one half of the mole doesn’t match the other. A normal mole is roughly symmetrical. If you drew a line down the center and the two sides look noticeably different in shape, that’s a red flag.
Border irregularity shows up as ragged, notched, or blurred edges. Rather than a clean, smooth outline, the pigment may seem to bleed or spread into the surrounding skin.
Color variation is one of the most telling signs. Instead of a single uniform shade of brown, a concerning mole may contain a mix of brown, tan, and black, sometimes with areas of white, gray, red, pink, or blue within the same spot.
Diameter matters, though size alone isn’t definitive. Most melanomas are larger than 6 millimeters wide, roughly the size of a pencil eraser. Melanomas can be smaller than this, but any mole that’s growing deserves attention.
Evolving is arguably the most important criterion. Any mole that has changed in size, shape, color, or texture over the past few weeks or months should be evaluated, even if it doesn’t check the other boxes.
The “Ugly Duckling” Sign
Beyond the ABCDE criteria, there’s a simpler screening concept that works well for people who have many moles. Your moles tend to look like each other. They share a general family resemblance in size, color, and shape. A melanoma often breaks that pattern, standing out as the one lesion that looks nothing like its neighbors. Dermatologists call this the “ugly duckling” sign. When scanning your skin, look for the outlier: the one mole that’s darker, larger, or just visually different from everything around it.
What Basal Cell Carcinoma Looks Like
Basal cell carcinoma is the most common skin cancer, and it looks nothing like what most people picture when they think of cancer. It typically shows up on sun-exposed areas, especially the head and neck, and grows slowly. On lighter skin, it often appears as a shiny, pearly, or translucent bump that may look pink or skin-colored. On darker skin tones, the same bump can appear brown or glossy black.
Not all basal cell carcinomas are bumps, though. Some look like a flat, scaly patch with or without a raised edge. Others resemble a brown, black, or blue lesion with a slightly raised, translucent border. One particularly easy-to-miss form looks like a white, waxy, scar-like area without a clear border. If you notice what looks like a scar in a spot where you were never injured, that’s worth getting checked.
What Squamous Cell Carcinoma Looks Like
Squamous cell carcinoma is the second most common skin cancer. It tends to appear as a firm bump or nodule that can be skin-colored, pink, red, brown, or black depending on your skin tone. Another common presentation is a flat sore topped with a scaly crust, or a rough, scaly patch on the lip that may develop into an open sore.
The hallmark of squamous cell carcinoma is persistence. A sore or scab that hasn’t healed in about two months, or a flat scaly patch that simply won’t go away, warrants a professional look. These can also develop on old scars or long-standing sores, appearing as a new raised area where the skin was previously damaged. Less commonly, they show up inside the mouth or on the genitals.
Melanoma Under the Nails
One form of melanoma hides in a place most people never think to check: under the fingernails or toenails. Called subungual melanoma, it typically starts as a dark streak or band running lengthwise along the nail. These pigmented lines are usually less than 3 millimeters wide at first but gradually widen over time. A key warning sign, known as the Hutchinson sign, is when the dark pigment spreads beyond the nail onto the surrounding skin of the fingertip or cuticle. This type of melanoma is more common on the thumb and big toe, and it disproportionately affects people with darker skin tones.
How to Do a Skin Self-Exam
A thorough self-check means examining your entire body, not just the areas you think get the most sun. Use a full-length mirror and a handheld mirror together to see your back, the backs of your legs, and your scalp. Pay special attention to the backs of your upper arms, which are commonly missed during self-exams. Check between your toes, on your soles, under your nails, and around your ears.
The goal isn’t to diagnose anything yourself. It’s to establish a baseline of what your skin looks like now so you can notice when something changes. Taking photos of moles you want to track can make it easier to spot subtle shifts in size or color over time. How often you should do this depends on your individual risk factors, so follow whatever schedule your doctor recommends.
What Happens During a Professional Check
A dermatologist screening goes beyond what you can do at home. One reason is a tool called a dermatoscope, essentially a magnifying lens with polarized light that lets the doctor see structures beneath the skin’s surface. Adding dermatoscopy to a standard visual exam improves melanoma detection sensitivity by about 16 percentage points, catching roughly 92% of melanomas compared to 76% with the naked eye alone.
If something looks suspicious, the next step is a biopsy, where a small sample of tissue is removed and examined under a microscope. There are a few types. A shave biopsy removes only a thin, superficial layer and is used for surface-level lesions. A punch biopsy takes a small circular core of deeper tissue. An excisional biopsy removes the entire suspicious area with a scalpel. Which one your doctor chooses depends on the size and location of the spot, and what they suspect it might be. The procedure is typically quick and done under local anesthesia in the office.
Why Early Detection Changes Everything
The survival gap between early and late-stage melanoma is dramatic. When melanoma is caught at stage I or II, before it has spread beyond the original site, the five-year relative survival rate is 97.6%. Once it reaches nearby lymph nodes (stage III), that drops to 60.3%. If it spreads to distant organs (stage IV), the rate falls to 16.2%. Basal cell and squamous cell carcinomas are far less likely to be fatal, but they can cause significant tissue damage and disfigurement if left to grow, especially on the face.
The practical takeaway is straightforward: any skin spot that is new and unusual, has changed recently, looks different from your other moles, or won’t heal after two months deserves professional evaluation. Most of the time it will turn out to be nothing. But when it isn’t nothing, catching it early is the single biggest factor in your outcome.