Skin cancer shows up as visible changes on your skin, and the specific signs depend on the type. The three most common types are basal cell carcinoma, squamous cell carcinoma, and melanoma, each with distinct warning signs. Knowing what to look for on your own body is one of the most effective ways to catch skin cancer early, when treatment is simplest.
Signs of Melanoma: The ABCDE Rule
Melanoma is the most dangerous form of skin cancer, but it’s also the one with the clearest visual checklist. Dermatologists use five features, summarized as ABCDE, to distinguish a suspicious mole from a harmless one:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles tend to be roughly symmetrical.
- Border: The edges are ragged, notched, or blurred rather than smooth. The pigment may bleed into the surrounding skin.
- Color: The color is uneven. You might see shades of brown, black, and tan mixed together, or patches of white, gray, red, pink, or blue within the same spot.
- Diameter: Most melanomas are larger than 6 millimeters (about the size of a pencil eraser) when diagnosed, though they can be smaller.
- Evolving: The mole has changed in size, shape, or color over the past few weeks or months. Any mole that’s noticeably different from what it looked like before deserves attention.
You don’t need all five features to be concerned. Even one or two, particularly a mole that’s evolving, is worth having examined.
The “Ugly Duckling” Sign
Beyond ABCDE, there’s a simpler instinct-based approach that works surprisingly well. The “ugly duckling” sign means one mole that looks obviously different from all the others on your body. Most people’s moles share a general family resemblance in color, size, and shape. A mole that stands out from its neighbors, whether it’s darker, larger, or just clearly unlike the rest, should raise suspicion for melanoma even if it doesn’t check every ABCDE box.
Signs of Basal Cell Carcinoma
Basal cell carcinoma is the most common skin cancer, and it looks quite different from melanoma. Rather than a changing mole, it typically appears as a new growth or a sore that won’t heal. The signs vary depending on skin tone:
- A shiny, translucent bump. On lighter skin, it looks pearly white or pink. On brown and Black skin, it often appears brown or glossy black. Tiny blood vessels may be visible on or near the surface. The bump may bleed and scab over repeatedly.
- A brown, black, or blue spot with a slightly raised, translucent border.
- A flat, scaly patch with or without a raised edge. These can grow quite large over time.
- A white, waxy, scar-like area without a clearly defined border. This type is easy to overlook because it doesn’t look like a typical “growth.”
The hallmark of basal cell carcinoma is a sore that bleeds, crusts over, seems to heal, and then opens up again. If you have a spot going through that cycle for more than a few weeks, that pattern alone is a red flag.
Signs of Squamous Cell Carcinoma
Squamous cell carcinoma is the second most common skin cancer. Its signs overlap somewhat with basal cell carcinoma but tend to have a rougher, scalier texture:
- A firm bump (nodule) that may be skin-colored, pink, red, brown, or black depending on your skin tone.
- A flat sore with a scaly crust that doesn’t go away.
- A new sore or raised area on an old scar.
- A rough, scaly patch on the lip that may develop into an open sore.
- A sore or rough patch inside the mouth, or a raised, wart-like growth on the genitals or anus.
The general rule: any sore or scab that hasn’t healed in about two months is worth getting checked. Squamous cell carcinoma can also develop in areas you might not think of as sun-exposed, including inside the mouth and on the lower lip.
Pre-Cancerous Spots to Watch
Actinic keratoses are rough, dry, scaly patches of skin that develop from years of sun exposure. They’re not cancer yet, but about 5% to 10% of them progress to squamous cell carcinoma if left untreated. They’re usually small (under an inch across) and can be pink, red, or brown. Some develop a hard, wart-like surface. They’re most common on the face, ears, scalp, forearms, and backs of the hands.
These spots often feel easier to detect by touch than by sight. If you run your fingers over your skin and notice a persistently rough or sandpapery patch, especially on sun-exposed areas, that’s the texture to pay attention to.
Skin Cancer in Hidden Locations
Not all skin cancers appear on obviously sun-exposed skin. Melanoma can develop under fingernails and toenails, a form called subungual melanoma. It typically shows up as a dark streak running the length of the nail. The streak is often less than 3 millimeters wide initially but gets wider over time. One important warning sign is discoloration of the skin surrounding the nail (known as Hutchinson sign), which suggests the pigment is spreading beyond the nail bed. This type is more common on the thumb and big toe and is disproportionately diagnosed in people with darker skin tones.
Skin cancer can also appear between the toes, on the soles of the feet, on the scalp, and on the genitals. These locations are easy to miss during a casual self-check, which is why a systematic approach matters.
Rare but Worth Knowing: Merkel Cell Carcinoma
Merkel cell carcinoma is uncommon but aggressive. It typically appears as a firm, painless, red or pink bump that grows rapidly, often doubling in size within a few weeks. The combination of those three features is the key signal: a bump that’s red, expanding fast, and doesn’t hurt. In a study of 195 cases, 88% of these tumors were painless despite their rapid growth, and 63% had expanded noticeably in just three months. It’s most common in people over 50, on sun-exposed skin, and in those with weakened immune systems.
How to Check Your Own Skin
A monthly self-exam is the simplest way to catch changes early. The best time is right after a bath or shower, and all you need is a full-length mirror and a hand mirror. Start by facing the full-length mirror and scanning your entire front, then turn around and check your back. Raise your arms and examine both sides of your body. Use the hand mirror to see areas you can’t view directly, like the back of your neck, scalp, and behind your ears.
Check your arms, including the undersides and between your fingers. Look at the tops and soles of your feet, between your toes, and at your toenails. Don’t skip your lips, the inside of your mouth, and your tongue. The goal isn’t to diagnose anything yourself. It’s to notice change. When you check regularly, you build a mental map of what your skin normally looks like, and anything new or different becomes obvious.