Skin cancer is the uncontrolled growth of abnormal cells in the outermost layer of skin, the epidermis. It is the most common form of cancer, with an estimated 112,000 new melanoma cases alone expected in the United States in 2026, and non-melanoma skin cancers numbering in the millions. Most skin cancers develop when ultraviolet radiation from sunlight or tanning beds damages the DNA inside skin cells, triggering mutations that cause those cells to multiply rapidly.
How UV Light Triggers Skin Cancer
Your skin cells contain DNA that controls how they grow, divide, and repair themselves. When UV radiation hits these cells, it can physically distort the DNA strand by fusing two neighboring molecules together. Under normal conditions, your body has repair systems that find and fix this damage. But when the damage accumulates faster than the repair systems can keep up, or when the repair process itself introduces errors, permanent mutations take hold.
The most common mutation swaps one DNA letter for another in a pattern that scientists recognize as a signature of UV damage. These mutations can disable the genes that tell a cell when to stop dividing. Once that brake is gone, the cell replicates without limit, forming a tumor. This is why skin cancer overwhelmingly appears on parts of the body that get the most sun exposure: the face, scalp, ears, lips, and backs of the hands.
The Three Main Types
The epidermis contains three types of cells, and each one can become cancerous. The type of cell involved determines which kind of skin cancer you have, how it behaves, and how serious it is.
Basal Cell Carcinoma
Basal cell carcinoma starts in the round cells that sit just beneath the skin’s surface. It is the most common skin cancer by a wide margin. It grows slowly and almost never spreads to distant parts of the body, but it can destroy surrounding tissue if left untreated. Basal cell carcinomas vary widely in appearance. They can look like shiny, pearly bumps (pink or gray), open sores that refuse to heal, red patches with a rough or sandpapery texture, or flat areas of thickened skin. Some have a rolled edge or visible blood vessels radiating outward like spokes on a wheel.
Squamous Cell Carcinoma
Squamous cell carcinoma begins in the thin, flat cells that form the skin’s outermost surface. It is the second most common type. These cancers most often appear on sun-exposed areas like the scalp, ears, lips, and hands, but they can develop anywhere, including inside the mouth, on the soles of the feet, or on the genitals. They typically look like firm nodules that may be pink, red, brown, or skin-colored, or flat scaly patches that don’t go away. A sore or scab that hasn’t healed after about two months is a warning sign. In people with darker skin tones, squamous cell carcinomas are more likely to develop on skin that doesn’t get much sun, such as the genitals.
Melanoma
Melanoma arises in melanocytes, the cells that produce the pigment giving skin its color. It is the third most common skin cancer but by far the most dangerous because it can spread quickly to other organs. When caught early and still confined to the original site, the five-year survival rate is above 99%. Once it has spread to distant parts of the body, that number drops to about 35%. The gap between those two figures is the strongest argument for regular skin checks.
Melanoma incidence rates have been climbing for decades. In men, the greatest increase has been on the torso. In women, it’s on the legs. Both are areas that get intense but intermittent sun exposure, the kind you get on a beach vacation rather than from daily outdoor work.
How to Spot Melanoma: The ABCDE Rule
The National Cancer Institute uses five visual features to help people identify suspicious moles early:
- Asymmetry: One half of the mole doesn’t match the other.
- Border: The edges are ragged, notched, or blurred, and pigment may spread into the surrounding skin.
- Color: The mole contains multiple shades of brown, black, or tan, or areas of white, gray, red, pink, or blue.
- Diameter: The spot is larger than 6 millimeters across (roughly the size of a pencil eraser), though melanomas can also be smaller.
- Evolving: The mole has visibly changed in size, shape, or color over recent weeks or months.
A mole doesn’t need to check every box to be concerning. Any single one of these features, especially “evolving,” is reason enough to have it examined.
Who Is Most at Risk
Fair skin is the most well-known risk factor because lighter skin contains less melanin, the pigment that absorbs and scatters UV radiation before it reaches DNA. But the relationship between skin tone and cancer risk is more nuanced than many people realize. Research has shown that the Fitzpatrick skin type scale, which classifies skin from type I (very fair, always burns) to type VI (deeply pigmented, never burns), can give people with darker skin a false sense of security. Skin cancers do occur in darker skin types, just at lower rates, and they’re often diagnosed later because neither patients nor doctors are looking for them.
Beyond skin tone, other factors raise your risk:
- History of sunburns: Even a few severe sunburns in childhood or adolescence significantly increase lifetime risk.
- Tanning bed use: Artificial UV sources cause the same DNA damage as sunlight.
- Many moles: Having a large number of moles, or moles that are unusual in shape or color, is associated with higher melanoma risk.
- Family history: A first-degree relative with melanoma increases your own risk.
- Weakened immune system: Organ transplant recipients and people on immune-suppressing medications develop skin cancers at higher rates.
Rare Forms of Skin Cancer
Beyond the big three, several uncommon types exist. Merkel cell carcinoma is one of the most aggressive. It starts in the touch-receptor cells near the base of the epidermis and usually appears on sun-exposed skin as a single, firm, dome-shaped lump that is red or violet. It grows fast, is painless, and tends to spread early. Other rare forms include sebaceous carcinoma, which develops in the oil glands of the skin (often on the eyelids), and dermatofibrosarcoma protuberans, a slow-growing tumor in the deeper layers of skin. These cancers are uncommon enough that many general practitioners may not immediately recognize them, which makes any new, persistent, or changing skin growth worth getting checked.
Treatment and Outlook
Treatment depends on the type, size, location, and stage of the cancer. For basal and squamous cell carcinomas, surgical removal is the standard approach. One specialized technique called Mohs surgery removes tissue one thin layer at a time, checking each layer under a microscope before cutting further. For aggressive or recurrent basal cell carcinomas on the face, this method has a five-year recurrence rate of just 3.3%, making it the most precise option for preserving healthy tissue in cosmetically sensitive areas.
For melanoma, the approach depends heavily on how deep the cancer has grown and whether it has spread. Early-stage melanoma is typically removed surgically with a margin of healthy skin around it. More advanced cases may require immunotherapy or targeted therapy to help the immune system attack cancer cells that have traveled beyond the original site.
The single most important factor in outcomes is timing. Localized melanoma, meaning it hasn’t spread beyond the skin where it started, has a five-year survival rate above 99%. That’s based on data from patients diagnosed between 2015 and 2021. The prognosis for basal and squamous cell carcinomas is even better when caught early, since these cancers rarely spread in the first place. Regular self-exams, knowing what your skin normally looks like, and having a professional skin check when something changes are the most effective tools for catching skin cancer while it’s still highly treatable.