A mole that could be skin cancer typically looks different from your other moles. It may be asymmetrical, have uneven color or ragged borders, measure larger than 6 millimeters (about the size of a pencil eraser), or change noticeably over weeks to months. But skin cancer doesn’t always show up as a dark, irregular mole. It can also appear as a pearly bump, a scaly patch, a pink spot, 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, when treatment is simplest.
The ABCDE Rule for Melanoma
Melanoma is the most dangerous form of skin cancer, and it’s the one most likely to develop in or near an existing mole. The standard checklist for spotting it is the ABCDE rule:
- Asymmetry: One half of the mole doesn’t match the other. Normal moles are roughly symmetrical.
- Border irregularity: The edges are ragged, notched, or blurred rather than smooth. Pigment may spread into the surrounding skin.
- Color that is uneven: Instead of one uniform shade, you see a mix of brown, tan, and black, sometimes with patches of white, gray, red, pink, or blue.
- Diameter: Most melanomas are larger than 6 millimeters wide (roughly a quarter inch), though they can start smaller.
- Evolving: The mole has changed in size, shape, color, or texture over the past few weeks or months. Any visible change in a mole is worth paying attention to.
A mole doesn’t need to check every box to be concerning. Even one of these features, especially evolution, is reason enough to have it examined.
The “Ugly Duckling” Approach
Your moles tend to share a family resemblance. They’re generally similar to each other in size, shape, and color, forming a pattern that’s unique to you. The “ugly duckling” method means scanning your skin for the mole that doesn’t fit the pattern. A dark, large mole stands out on someone whose other moles are small and light. A reddish, flat spot stands out on someone whose moles are all raised and brown. If one mole looks like it doesn’t belong with the rest, that’s the one to get checked.
Nodular Melanoma: A Faster-Growing Type
Not all melanomas spread outward across the skin first. Nodular melanoma grows downward into the skin quickly, and it can change noticeably in days or weeks rather than months. It often appears as a raised, dome-shaped bump that feels firm to the touch. It may be dark brown or black, but it can also be red or skin-colored, which makes it easy to dismiss as a pimple or cyst.
Because it grows fast, the standard ABCDE criteria sometimes miss it. A simpler set of signs applies here: elevation (raised above the skin), firmness, and rapid growth. Any new bump that is firm and getting bigger quickly deserves prompt attention.
Melanoma That Isn’t Dark
About 5 percent of melanomas are amelanotic, meaning they lack the dark pigment most people associate with skin cancer. These appear as pink or red spots on the skin and are easily confused with a bug bite, rash, or harmless blemish. Because they don’t look like what people expect skin cancer to look like, amelanotic melanomas are often diagnosed at a later stage than their darker counterparts. If you have a pink or reddish spot that persists for several weeks, doesn’t heal, or slowly grows, it’s worth having a professional look at it.
Melanoma Under the Nail
Skin cancer can develop in places you wouldn’t think to check. Subungual melanoma forms under a fingernail or toenail, most commonly appearing as a dark brown or black vertical streak running from the base of the nail to the tip. The streak is typically irregular in color, with varying shades of blackish brown, and it may start narrow (under 3 millimeters wide) before widening over time, usually from the base of the nail first.
As it progresses, the nail may crack, split, or lift away from the nail bed. The skin surrounding the nail can become discolored too, a sign known as the Hutchinson sign. This type of melanoma is more common on the thumb and big toe and occurs at higher rates in people with darker skin tones.
What Basal Cell Carcinoma Looks Like
Basal cell carcinoma is the most common skin cancer, and it looks nothing like a mole. On lighter skin, it typically appears as a shiny, translucent bump with a pearly white or pinkish sheen. You can almost see through the surface. Tiny blood vessels may be visible on or around it. On darker skin, the same bump often looks brown or glossy black. These bumps tend to bleed, then scab over, then bleed again in a repeating cycle.
Basal cell carcinoma grows slowly. Research estimates it takes roughly 8 to 11 years from the time a basal cell carcinoma begins forming at the cellular level to reach a size that’s clinically detectable, and its tumor volume doubles roughly every 4 to 6 months after that. This slow pace means people often assume the bump is harmless, but it will keep growing and can eventually damage surrounding tissue if left alone.
What Squamous Cell Carcinoma Looks Like
Squamous cell carcinoma is the second most common skin cancer. It often appears as a firm bump or nodule that can be skin-colored, pink, red, brown, or black depending on your skin tone. It may also show up as a flat sore with a scaly crust that doesn’t fully heal, a rough scaly patch on the lip, or a new raised area developing on an old scar. In some cases it resembles a wart.
These lesions tend to appear on sun-exposed areas like the face, ears, hands, and forearms, but they can also develop inside the mouth or on the genitals. The hallmark is a sore or rough patch that crusts, bleeds, heals partially, then returns.
Harmless Growths That Mimic Cancer
Seborrheic keratoses are among the most common benign skin growths, and they can look alarming. They’re waxy, slightly raised, and sometimes dark enough to resemble melanoma at first glance. The key difference is texture: seborrheic keratoses have a distinctive “stuck-on” appearance, as though someone glued a waxy scab to the skin surface. They’re painless, don’t bleed on their own, and tend to stay flat. Melanomas, by contrast, are more likely to have irregular color mixing, blurred borders, and visible changes over time.
Even with these guidelines, the overlap between benign and malignant growths can be subtle. A mole or spot that is new, changing, bleeding without injury, or simply looks different from everything else on your skin is the one most worth having a dermatologist examine. Early skin cancers are almost always treatable when caught before they grow deeper.