There are three main types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma. Together, these account for the vast majority of skin cancer diagnoses. A handful of rare skin cancers also exist, including Merkel cell carcinoma and Kaposi sarcoma. Each type starts in a different kind of skin cell, behaves differently, and carries a different level of risk.
Basal Cell Carcinoma
Basal cell carcinoma (BCC) is the most common skin cancer by a wide margin. It begins in basal cells, which sit in the deepest layer of the outer skin and continuously produce new skin cells as old ones die off. BCC typically looks like a flesh-colored round growth, a pearl-like bump, or a pinkish patch of skin. It usually develops on areas that get regular sun exposure, like the face, scalp, ears, and neck, though it can appear anywhere.
BCC grows slowly compared to other skin cancers, and it rarely spreads to distant parts of the body. That doesn’t make it harmless. Left untreated, it can grow deep enough to reach nerves and bone, causing significant damage and disfigurement. Years of frequent sun exposure or indoor tanning are the primary drivers. Most people who develop BCC are diagnosed in middle age or later, but it’s becoming more common in younger adults as well.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) is the second most common skin cancer. It starts in squamous cells, the flat cells that make up the outer surface of your skin. SCC often looks like a red, firm bump, a scaly patch, or a sore that heals and then reopens. It tends to show up on skin that gets frequent sun exposure: the rim of the ear, face, neck, arms, chest, and back.
SCC is more aggressive than BCC. It can grow deep into the skin and, in some cases, spread to lymph nodes or other organs. It also frequently develops from a precancerous condition called actinic keratosis, which appears as rough, scaly, sandpaper-like patches on sun-exposed skin. Many people mistake actinic keratosis for a scab or sore that won’t heal, or even an acne breakout. Most cases are treated before they progress, but untreated actinic keratosis carries a real risk of becoming squamous cell carcinoma.
Melanoma
Melanoma develops in melanocytes, the cells that produce the pigment giving your skin its color. It accounts for a smaller share of skin cancer diagnoses than BCC or SCC, but it’s the most dangerous because of its tendency to spread to other parts of the body. An estimated 112,000 new cases will be diagnosed in the U.S. in 2026, and roughly 2.2 percent of Americans will be diagnosed with melanoma at some point in their lifetime.
Melanoma can appear as a new dark spot on the skin or develop within a mole you already have. The standard way to evaluate a suspicious spot is the ABCDE method:
- Asymmetry: one half of the spot doesn’t match the other
- Border: the edges are ragged, notched, or blurred, sometimes with pigment spreading into surrounding skin
- Color: multiple shades are present, including black, brown, tan, white, gray, red, pink, or blue
- Diameter: the spot is larger than about 6 millimeters (roughly the size of a pencil eraser), though melanomas can be smaller
- Evolving: the mole has changed in size, shape, or color over recent weeks or months
Not every melanoma checks all five boxes, but any one of these features is worth having evaluated. Early-stage melanoma that hasn’t spread beyond the skin has a very high survival rate. Once it reaches the lymph nodes or distant organs, treatment becomes far more complex.
How UV Radiation Causes Skin Cancer
Sunlight delivers two types of ultraviolet radiation that damage skin cells. UVB rays are mostly absorbed by the outermost layer of skin and directly damage DNA by creating errors in the genetic code. UVA rays penetrate deeper, reaching the lower layers of skin where melanocytes live. UVA delivers up to 100 times more energy than UVB to those deeper layers.
What makes melanoma biology particularly tricky is that melanin, the pigment meant to protect you from UV damage, can actually work against you. Melanin absorbs UV energy and normally neutralizes it, but it can also act as a chemical trigger that generates additional DNA damage. One especially unusual finding: after UVA exposure ends, a type of melanin called pheomelanin (the kind found in higher amounts in people with red hair and fair skin) continues producing DNA damage for hours in the dark. This “dark damage” pathway helps explain why fair-skinned individuals face a higher melanoma risk even with limited sun exposure.
Rare Skin Cancers
Several uncommon skin cancers exist beyond the big three. Merkel cell carcinoma is one of the most notable. It’s a rare, aggressive cancer that most often affects people over 50. Unlike BCC or SCC, Merkel cell carcinoma tends to grow fast and spread quickly. The first sign is typically a painless bump on the skin that grows rapidly and whose two sides don’t match. In white patients, it usually appears on the head or neck. In Black patients, it more commonly shows up on the legs. The bump can look pink, purple, red-brown, or match the surrounding skin tone, which sometimes delays recognition.
Other rare types include Kaposi sarcoma (linked to a specific virus and most common in people with weakened immune systems), sebaceous carcinoma (which starts in the oil glands, often near the eyelids), and dermatofibrosarcoma protuberans (a slow-growing cancer in the deeper layers of skin). These are uncommon enough that most dermatologists see only a handful of cases in their careers.
How Skin Cancer Is Staged
Once a skin cancer is diagnosed, doctors assign a stage from 0 to IV based on three factors: the size and depth of the primary tumor, whether cancer has reached nearby lymph nodes, and whether it has spread to distant parts of the body. Stage 0 means abnormal cells are present but haven’t invaded deeper tissue. Stages I through III reflect increasingly larger tumors or local spread. Stage IV means the cancer has reached distant organs.
Staging matters because it determines treatment and outlook. A small, shallow BCC is a completely different situation from a stage IV melanoma, even though both fall under “skin cancer.”
Treatment Options
Most basal cell and squamous cell carcinomas are treated with surgery. For cancers on the face, neck, fingers, toes, or other sensitive areas, a technique called Mohs surgery is considered the gold standard. The surgeon removes thin layers of tissue one at a time, examining each layer under a microscope before deciding whether to take more. This preserves as much healthy skin as possible while achieving cure rates up to 99 percent for common skin cancers. Mohs surgery is especially useful for large tumors, aggressive growth patterns, or cancers that have come back after a previous treatment.
Smaller or less aggressive skin cancers may be treated with simpler excision, freezing, or topical treatments applied directly to the skin. For advanced melanoma or skin cancers that have spread, immunotherapy has become a major treatment option. These drugs help the immune system recognize and attack cancer cells, and they’ve dramatically improved outcomes for metastatic melanoma over the past decade. Radiation therapy is sometimes used when surgery isn’t practical or as a follow-up to reduce the chance of recurrence.
People with weakened immune systems, such as organ transplant recipients, face a significantly higher risk of developing skin cancer and often need more aggressive monitoring and treatment. For them, even common skin cancers like SCC can behave more aggressively than they would in someone with a healthy immune system.