The four types of skin cancer are basal cell carcinoma, squamous cell carcinoma, melanoma, and Merkel cell carcinoma. The first two are by far the most common, accounting for roughly 6.1 million treatments in U.S. adults each year combined. Melanoma is less common but more dangerous, and Merkel cell carcinoma is rare but aggressive. Each type looks different on the skin, behaves differently in the body, and carries a different level of risk.
Basal Cell Carcinoma
Basal cell carcinoma (BCC) is the most frequently diagnosed skin cancer. It develops in the basal cells at the bottom of your outer skin layer, and it grows slowly. BCC almost never spreads to distant parts of the body, but it can damage surrounding tissue if left untreated for months or years.
BCC usually shows up on parts of the body that get the most sun: the head, face, and neck. It often looks like a slightly transparent or pearly bump. On lighter skin, the bump tends to appear white or pink. On darker skin, it can look brown or glossy black. You might notice tiny blood vessels running through it, or it may bleed and scab over repeatedly. Some BCCs look like flat, scaly patches that grow larger over time, and others resemble a white, waxy, scarlike area with no clear border. The hallmark sign is a sore that won’t fully heal.
When caught early, BCC is highly treatable. A surgical technique called Mohs surgery, where tissue is removed layer by layer and examined under a microscope during the procedure, has a recurrence rate of only about 2% for previously untreated tumors over five years.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) is the second most common skin cancer. It forms in the flat squamous cells that make up the outer surface of your skin. SCC is more likely than BCC to grow into deeper layers and, in uncommon cases, spread to lymph nodes or other organs.
SCC can appear as a firm bump or nodule that may be pink, red, brown, or black depending on your skin tone. It can also show up as a flat sore with a scaly crust, a rough patch on the lip that becomes an open sore, or a raised wartlike growth. One distinctive feature: SCC sometimes develops on old scars or chronic wounds, not just sun-exposed skin. It can also form inside the mouth or on the genitals.
SCC often starts from precancerous patches called actinic keratoses, which are rough, sandpaper-textured spots caused by years of sun exposure. Research published in the Journal of the American Academy of Dermatology estimated that individual actinic keratosis lesions progress to invasive squamous cell carcinoma at an average rate of about 8% across studies. That rate is low per lesion, but people who have many of these patches face a meaningful cumulative risk, which is why dermatologists typically treat them early.
Melanoma
Melanoma develops in the cells that give skin its color. It accounts for a small fraction of skin cancer diagnoses but causes the majority of skin cancer deaths, because it is far more likely to spread to other organs. When caught while still localized to the skin, the five-year survival rate is 97.6%. Once it reaches nearby lymph nodes, that drops to 60.3%, and if it spreads to distant organs, it falls to 16.2%. Early detection changes the outcome dramatically.
The most useful tool for spotting melanoma at home is the ABCDE checklist from the National Cancer Institute:
- Asymmetry: one half of the mole doesn’t match the other.
- Border: the edges are ragged, notched, or blurred, and pigment may spread into surrounding skin.
- Color: the color is uneven, with shades of brown, black, 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.
Melanoma can appear anywhere on the body, including areas that rarely see the sun. It can develop in an existing mole or appear as a brand-new spot. If your dermatologist suspects melanoma, they will typically perform an excisional biopsy, removing the entire suspicious area rather than just a sample, to ensure the full depth and margin of the lesion can be evaluated.
Merkel Cell Carcinoma
Merkel cell carcinoma is the rarest of the four types, but it’s also the most aggressive. It develops in Merkel cells, which sit near nerve endings in your skin and are involved in the sense of touch. This cancer grows fast and has a high tendency to spread.
It usually appears as a firm, painless bump on sun-exposed skin. The bump can look pink, purple, red-brown, or skin-colored, and its two sides often don’t match. On white skin, it most commonly shows up on the head or neck. On Black skin, it appears more often on the legs. The key warning sign is speed: if a bump is growing noticeably over days or weeks, or bleeds easily from minor contact like washing or shaving, that warrants prompt evaluation.
Most cases occur in people over 50. The major risk factors are long-term sun exposure, a weakened immune system, and lighter skin that burns easily. A virus called Merkel cell polyomavirus, which lives on the skin of most people without causing problems, plays a role in triggering many cases.
How BCC and SCC Differ From Melanoma and Merkel Cell
Dermatologists sometimes split skin cancers into two broad categories. BCC and SCC are called nonmelanoma or keratinocyte cancers. They are common, usually slow-growing, and rarely life-threatening when treated. Melanoma and Merkel cell carcinoma are less common but far more dangerous because of their tendency to metastasize. This distinction matters practically: the urgency of treatment and the follow-up monitoring schedule are more intensive for melanoma and Merkel cell carcinoma.
When a dermatologist biopsies a suspicious spot, the suspected cancer type guides the approach. For possible BCC or SCC, a punch biopsy (a small cylindrical sample) or shave biopsy (slicing off the surface layer) is usually enough. For suspected melanoma, the preference is to remove the entire lesion so pathologists can assess how deep it goes.
Reducing Your Risk
Ultraviolet radiation is the single biggest modifiable risk factor for all four types. The CDC recommends broad-spectrum sunscreen with an SPF of at least 15 before going outside, reapplied every two hours and after swimming, sweating, or toweling off. Protective clothing, shade during peak sun hours, and avoiding tanning beds all reduce cumulative UV damage.
Regular skin self-checks are just as important as sun protection. Familiarize yourself with your existing moles and spots so you can notice changes. Any new growth that bleeds, doesn’t heal, changes shape or color, or grows rapidly is worth having evaluated, regardless of whether it fits neatly into the descriptions above. Skin cancers don’t always look textbook, and catching them early is consistently the factor that matters most for outcomes.