Skin cancer shows up in several distinct ways depending on the type, but the core warning signs are changes to existing moles, new growths that look unusual, or sores that refuse to heal. About 2.2% of people will be diagnosed with melanoma alone during their lifetime, and non-melanoma skin cancers like basal cell and squamous cell carcinoma are far more common. The good news is that most skin cancers are highly treatable when caught early, and you can spot many of the warning signs yourself at home.
The ABCDE Rule for Melanoma
Melanoma is the most dangerous form of skin cancer, but it also gives you visible clues. Dermatologists use a five-letter system to help you evaluate any mole or pigmented spot on your body:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles tend to be roughly symmetrical.
- Border: The edges are uneven, blurred, ragged, or notched instead of smooth and well-defined.
- Color: The spot contains multiple colors or shades, such as brown mixed with black, red, white, or blue. Healthy moles are usually a single uniform color.
- Diameter: The spot is larger than a pencil eraser (about 6 millimeters). Melanomas can be smaller, but size matters when combined with other signs.
- Evolving: Any change in size, shape, color, or height. New symptoms like itching, bleeding, or scabbing also count.
A mole doesn’t need to check every box to be suspicious. Even one of these features, particularly evolution over time, is enough reason to have it looked at.
The Ugly Duckling Sign
Sometimes the simplest method is the most useful. The “ugly duckling” approach means scanning all your moles as a group and looking for the one that doesn’t fit the pattern. Most of your moles will share a general family resemblance in color, size, and shape. If one mole stands out from the rest, looking noticeably different from its neighbors, that’s the ugly duckling, and it deserves closer attention. This technique works well as a quick complement to the ABCDE rule, especially if you have many moles and aren’t sure where to start.
What Non-Melanoma Skin Cancers Look Like
Basal cell carcinoma is the most common skin cancer, and it often doesn’t look like what people expect. Rather than a dark mole, it typically appears as a shiny, translucent bump with a pearly or waxy surface. On lighter skin, it may look pink or white. You can sometimes see tiny blood vessels through the surface. Another common form is a flat, scaly patch with or without a raised edge that slowly grows larger over time.
Squamous cell carcinoma often appears as a firm, red nodule or a flat sore with a scaly, crusted surface. It can develop anywhere but favors sun-exposed areas like the face, ears, neck, hands, and arms. Both basal and squamous cell cancers share one hallmark trait: they show up as sores or spots that don’t heal. If you have a wound or crusty patch that bleeds, scabs over, and then returns repeatedly over several weeks, that cycle of non-healing is a red flag regardless of what the spot looks like otherwise.
Signs on Darker Skin Tones
Skin cancer in people with darker skin often appears in places most screening advice overlooks. A type called acral melanoma develops on the palms, soles of the feet, and under the nails, areas that get little sun exposure. These spots typically show up as dark brown or black patches on the palms or soles. Under a nail, the cancer often looks like a dark pigmented streak running the length of the nail that may extend to the surrounding skin fold or cause the nail to split.
Some of these lesions can also be pink or red rather than dark, making them easy to mistake for a bruise, fungal infection, or minor injury. The standard ABCDE criteria are less reliable for these cancers because acral lesions can look symmetrical and uniformly pigmented in early stages. An alternative set of warning signs uses the acronym CUBED: colored lesions that are unusual, bleeding, of uncertain diagnosis, enlarged, or deteriorating with delayed healing. If you notice any persistent spot on your hands, feet, or nails that doesn’t heal or slowly changes, it warrants evaluation regardless of your skin tone.
How to Do a Full-Body Self-Check
A thorough skin check takes about 10 to 15 minutes once you know the routine. The goal the first time is to learn your baseline: the existing pattern of moles, freckles, and marks across your entire body. After that, you’re looking for anything new or different.
Start standing in front of a full-length mirror. Check your face, ears, neck, chest, and belly. Women should lift the breasts to check underneath. Raise your arms and examine your underarms, then work down both arms to the tops and palms of your hands, between your fingers, and under each fingernail.
Sit down and check the front of your thighs, shins, tops of your feet, between your toes, and under your toenails. Then use a hand mirror to examine the bottoms of your feet, your calves, and the backs of your thighs, one leg at a time. For your scalp, part your hair in sections or use a blow dryer to move it aside. A partner can help with your back, the backs of your ears, and other hard-to-see areas.
Taking photos of spots you want to track makes it much easier to notice subtle changes over months. A simple phone photo with good lighting works fine. The key is consistency: check the same spots in the same lighting so real changes don’t get lost.
How Often to Check
The American Cancer Society recommends periodic skin checks as part of routine health exams for adults over 20. If you have a family history of melanoma (roughly 10% of melanoma patients do), monthly self-exams and regular dermatologist visits are recommended. People at high risk due to fair skin, light eyes, red or light hair, many moles, a weakened immune system, or a personal history of skin cancer benefit from professional skin exams every six months. For everyone else, a monthly self-check at home and an annual skin exam with a dermatologist is a reasonable schedule.
What Happens If Something Looks Suspicious
Only a biopsy can confirm or rule out skin cancer. No doctor can diagnose it by sight alone. If your dermatologist sees something concerning, they’ll remove a small sample of tissue and send it to a lab for analysis. The procedure is done in the office with local numbing and takes only minutes.
The type of biopsy depends on the spot. A shave biopsy removes a thin layer from the surface and usually doesn’t require stitches. A punch biopsy uses a small circular tool to take a deeper core of tissue and may need one or two stitches. An excisional biopsy removes the entire suspicious area along with a margin of healthy skin and typically requires stitches. Your dermatologist will choose the method based on the size, depth, and location of the lesion. Results usually come back within one to two weeks.
If the biopsy is positive, the next steps depend on the type and stage. Most basal and squamous cell cancers are curable with outpatient procedures when caught before they spread. Melanoma treatment becomes more complex at later stages but has excellent outcomes when detected early, which is exactly why self-checks matter.