Skin cancer shows up in several distinct ways depending on the type, but the core skill is the same: you’re looking for spots that are new, changing, or visually different from everything else on your skin. Melanoma, the most dangerous form, has well-defined warning signs you can learn to spot. The two more common types, basal cell carcinoma and squamous cell carcinoma, look quite different from melanoma and from each other. Here’s what to look for with each one.
The ABCDE Rule for Melanoma
Melanoma is the type most people worry about, and for good reason: an estimated 112,000 new cases will be diagnosed in 2026, with about 8,500 deaths. The good news is that early melanomas have recognizable features. Dermatologists use a five-letter checklist called the ABCDE rule:
- Asymmetry: One half of the mole doesn’t match the other half.
- Border: The edges are ragged, notched, or blurred rather than smooth and round. Pigment may spread into the surrounding skin.
- Color: Instead of one uniform shade, you see a mix of brown, tan, black, or even patches of white, gray, red, pink, or blue.
- Diameter: Most melanomas are larger than 6 millimeters across (roughly the size of a pencil eraser), though they can be smaller.
- Evolving: The mole has changed in size, shape, or color over the past few weeks or months.
You don’t need all five features to be present. A single one, especially “evolving,” is enough reason to have a dermatologist take a closer look. Any mole that’s noticeably changing deserves attention, even if it doesn’t check every other box.
The Ugly Duckling Sign
Beyond the ABCDE criteria, there’s a simpler, more intuitive approach: look for the outlier. Most of your moles tend to resemble each other in color, size, and shape. The “ugly duckling” is the one mole that looks nothing like its neighbors. It might be darker, larger, or just visually out of place. That mismatch alone is a reason to get it checked. This method is especially helpful when you have many moles and can’t easily apply the ABCDE criteria to each one individually.
Basal Cell Carcinoma: The Most Common Type
Basal cell carcinoma is far more common than melanoma and rarely spreads to distant parts of the body, but it can grow into surrounding tissue and cause real damage if ignored. It typically appears on sun-exposed areas like the face, ears, neck, and scalp. What makes it tricky is that it often doesn’t look like what people picture when they think of “cancer.”
On lighter skin, the classic sign is a shiny, pearly, or translucent bump that may have tiny visible blood vessels running through it. It can look pink or skin-colored. On brown or Black skin, the same bump often appears brown or glossy black. Other presentations include a flat, scaly patch with a raised edge, a brown or blue lesion with a translucent border, or a white, waxy, scar-like area with no clear boundary. These bumps commonly bleed, scab over, and then seem to heal, only to bleed again. That cycle of bleeding and scabbing that never fully resolves is one of the most reliable warning signs.
Squamous Cell Carcinoma: Rough and Persistent
Squamous cell carcinoma is the second most common skin cancer. It tends to appear on areas that get chronic sun exposure: the face, ears, hands, and forearms. It can also develop on the lips, inside the mouth, and on the genitals.
The hallmark feature is a firm, raised bump or a flat sore with a thick, scaly crust. The bump may be skin-colored, pink, red, brown, or black depending on your skin tone. A rough, scaly patch on the lip that progresses into an open sore is a particularly characteristic presentation. Pay attention to any new sore or raised area that develops on an old scar or wound, as this is another common pattern. Unlike a cut or scrape, these lesions don’t heal within a few weeks. Persistence is the key signal.
Precancerous Spots to Watch
Actinic keratoses are rough, scaly patches caused by years of sun exposure. They’re not cancer yet, but they can progress into squamous cell carcinoma over time. Most are treated before they reach the cancer stage. You’ll typically find them on the face, scalp (especially in people with thinning hair), backs of the hands, and forearms. They feel like sandpaper, and they’re often easier to feel than to see. If you notice rough patches that persist for weeks and don’t respond to moisturizer, have a dermatologist evaluate them.
Signs on Darker Skin Tones
Skin cancer can occur in people of all racial and ethnic backgrounds, but it often looks different on darker skin and frequently appears in locations people don’t think to check. Acral lentiginous melanoma, a subtype that occurs equally across all races, is the most common form of melanoma in people of color. It develops on the palms of the hands, the soles of the feet, and under the fingernails or toenails.
On palms and soles, the first sign is a dark brown or black discoloration that may look like a bruise or stain. Unlike an actual bruise, it doesn’t fade over time and gradually grows larger. Under the nails, a subtype called subungual melanoma appears as dark vertical streaks or discolorations running the length of the nail bed. It’s often mistaken for a fungal infection or dried blood. As it advances, it can cause the nail to crack or break. If you have a dark streak under a nail that you can’t explain with a recent injury, and especially if it’s widening, that warrants evaluation.
How to Do a Full Skin Check at Home
The American Academy of Dermatology recommends checking your skin regularly using a systematic approach so you don’t miss areas. A well-instructed person can identify suspicious moles with reasonable accuracy, though skin cancer specialists are significantly more precise at deciding what needs a biopsy. Home checks aren’t a substitute for professional exams, but they’re how most skin cancers first get noticed.
Start by standing in front of a full-length mirror and examining your body from the front and back. Raise your arms and check both sides. Then bend your elbows and carefully look at your forearms, underarms, fingernails, and palms. Next, examine the backs of your legs, the spaces between your toes, your toenails, and the soles of your feet. Use a hand mirror to check the back of your neck and scalp, parting your hair for a closer look. Finish by using the hand mirror to see your back and buttocks.
The whole process takes about 10 minutes. What you’re building over time is a mental map of your skin so that changes become obvious. Taking photos of moles you want to track can make it easier to notice subtle shifts in size, shape, or color over months.
What Happens if Something Looks Suspicious
If a dermatologist sees something concerning, the next step is a biopsy, which means removing a small sample of tissue to examine under a microscope. For suspected melanoma, the preferred approach is to remove the entire lesion with a small margin of normal skin around it. This gives the pathologist the complete picture. Partial samples can underestimate how deep a melanoma goes, which happens in roughly 1 in 5 cases where only part of the lesion is sampled.
For suspected basal cell or squamous cell carcinomas, a surface-level sample or a small circular punch through the skin is often sufficient for diagnosis. The biopsy itself is done with local numbing and typically takes just a few minutes. Results usually come back within one to two weeks.
The most important thing to understand about skin cancer detection is that no single feature is definitive on its own. What matters is the pattern: new growths that don’t behave like normal skin, existing spots that change, and sores that refuse to heal. When you notice something that fits those descriptions, getting it looked at promptly is what makes the difference between a minor procedure and a more complicated one.