There are three main kinds of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma. Basal cell and squamous cell carcinomas are by far the most common, accounting for roughly 6.1 million treatments in adults each year in the U.S. alone. Melanoma is less common but significantly more dangerous. A handful of rare skin cancers also exist, including Merkel cell carcinoma and Kaposi sarcoma.
Basal Cell Carcinoma
About 8 out of 10 skin cancers are basal cell carcinomas (BCC), making this the most common type. It starts in the basal cell layer, the deepest part of your skin’s outer surface. BCCs typically appear on sun-exposed areas like the face, head, neck, and arms, and they grow slowly.
What it looks like depends on the subtype. The most common form, nodular BCC, appears as a round, pimple-like bump with tiny visible blood vessels on its surface. It may look slightly see-through or pearly, with a color ranging from pinkish to brown or blue-black. Other forms include flat, scaly patches that are slightly lighter than the surrounding skin, or scar-like lesions that slowly expand over time.
BCC very rarely spreads to other parts of the body, which is why many people think of it as the “least dangerous” skin cancer. That framing can be misleading, though. Left untreated, BCC can grow into bone and tissue beneath the skin, causing serious local damage. It also has a tendency to come back in the same spot if not completely removed.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) accounts for roughly 2 out of 10 skin cancers. It originates in the flat cells of your skin’s outermost layer and commonly shows up on the face, ears, neck, lips, arms, and backs of the hands. Unlike BCC, SCC can also develop in scars, chronic skin sores, or on mucous membranes like the inside of the mouth or the genitals.
SCC often appears as a firm bump (which can be skin-colored, pink, red, or brown), a flat sore with a scaly crust, or a rough, scaly patch on the lip that may turn into an open sore. It is more aggressive than basal cell carcinoma. Untreated SCC can grow into deeper layers of skin, spread to lymph nodes or other organs, and in uncommon cases be fatal.
Actinic Keratosis: A Precancerous Warning
Actinic keratosis is not cancer itself, but it is a precancerous lesion directly linked to SCC. These rough, scaly patches develop on sun-exposed skin, most often in older adults. About 82% of cutaneous squamous cell carcinomas arise from actinic keratoses. The progression rate for any single lesion is low on a year-to-year basis, but people with multiple lesions face a cumulative risk that climbs over time, reaching about 2.5% within four years of diagnosis. If your doctor identifies actinic keratosis, treating it early is one of the most straightforward ways to prevent squamous cell carcinoma.
Melanoma
Melanoma develops from melanocytes, the cells that give skin its pigment. It is far less common than basal or squamous cell cancers, but it is the most likely to spread and become life-threatening. Caught early, the picture is very different from late-stage disease: the five-year survival rate for localized melanoma (stages I and II) is 97.6%. Once it reaches nearby lymph nodes, that drops to 60.3%. If it spreads to distant organs, survival falls to 16.2%.
Melanoma has four main subtypes, each with distinct behavior:
- Superficial spreading melanoma is the most common, representing about 70% of cases. It grows outward across the skin surface for months or years before pushing deeper. It appears as a flat or slightly raised brown lesion with uneven color and irregular borders, and can occur anywhere on the body.
- Nodular melanoma accounts for about 15% of cases and is the most aggressive common subtype. It invades deeper tissue soon after appearing, typically as a dark, dome-shaped bump that can resemble a blood blister.
- Acral-lentiginous melanoma makes up roughly 8% of melanomas and appears on the palms, soles, or under the nails. It is the most common melanoma subtype in people with darker skin tones and is similarly aggressive to nodular melanoma.
- Lentigo maligna melanoma accounts for about 5% of cases. It develops on chronically sun-exposed skin in older adults and may exist as a large, flat, discolored patch for years before becoming invasive.
How to Spot a Suspicious Mole
The ABCDE rule, developed by the National Cancer Institute, is the standard framework for evaluating moles:
- Asymmetry: One half of the mole doesn’t match the other.
- Border: The edges are ragged, notched, or blurred, sometimes with pigment spreading into surrounding skin.
- Color: The color is uneven, with mixtures of black, brown, tan, white, gray, red, pink, or blue.
- Diameter: The mole is larger than 6 millimeters (about the size of a pencil eraser), though melanomas can sometimes be smaller.
- Evolving: The mole has changed in size, shape, or color over recent weeks or months.
Any one of these features is worth having checked. A mole that checks multiple boxes warrants prompt evaluation.
Rare Skin Cancers
Merkel cell carcinoma is a rare, fast-growing cancer that typically appears as a firm, painless, shiny bump that is flesh-colored or bluish-red. It most often affects sun-exposed skin on the face and arms. The average age at diagnosis is 75, and people with weakened immune systems are at higher risk regardless of age. Despite being uncommon, Merkel cell carcinoma is considered more dangerous than the common skin cancers because of how quickly it can spread.
Kaposi sarcoma looks different from most skin cancers. It causes flat or slightly raised patches that are pink, red, or purple, and it can spread to internal organs. It is caused by a specific virus (human herpesvirus type 8) and occurs most often in people with suppressed immune systems, particularly those with advanced HIV or those taking immunosuppressant drugs after organ transplantation. A classic form also affects older men of Mediterranean, Eastern European, or Ashkenazi Jewish descent.
Who Is Most at Risk
Ultraviolet radiation exposure is the dominant risk factor for all major skin cancers. Your individual risk depends heavily on your skin’s natural response to sunlight. Dermatologists classify this on a six-point scale: people with very pale skin that always burns and never tans (often those with red hair and freckles) face the highest UV sensitivity. Those with fair skin that burns easily and tans minimally are close behind. Risk decreases progressively through medium and olive skin tones. People with deeply pigmented, dark brown to black skin that rarely or never burns have the lowest UV-related risk.
But lower risk is not zero risk. Acral-lentiginous melanoma, the subtype that appears on palms, soles, and nail beds, does not depend on sun exposure and occurs across all skin tones. Other risk factors that apply broadly include a history of blistering sunburns, use of tanning beds, a weakened immune system, a personal or family history of skin cancer, and having a large number of moles.