Skin cancer is the uncontrolled growth of abnormal cells in the skin, triggered when DNA damage (most often from ultraviolet radiation) overwhelms the body’s ability to repair itself. It is the most common type of cancer, with melanoma alone expected to account for 112,000 new diagnoses in the United States in 2026. There are several types, ranging from slow-growing and highly treatable to aggressive and potentially life-threatening.
How Skin Cancer Develops
Your skin cells are constantly dividing to replace old or damaged tissue. Each time a cell divides, it copies its DNA. Ultraviolet radiation from the sun or tanning beds can damage that DNA directly, creating errors the cell then has to fix before it divides again.
Healthy cells have built-in checkpoints. When they detect DNA damage, they pause the division process and attempt repairs. If the damage is too severe, the cell destroys itself to prevent passing the error along to new cells. Skin cancer develops when these safety mechanisms fail. A cell with damaged DNA slips through the checkpoints, divides anyway, and passes its mutations to daughter cells. Over time, those mutated cells multiply without restraint, forming a tumor.
The Three Main Types
Basal Cell Carcinoma
Basal cell carcinoma (BCC) is the most common form. It typically appears as a shiny, pearly bump with a smooth surface, rolled borders, and tiny visible blood vessels on the surface. Some variants look brown, blue, or black due to pigment within the growth, while superficial BCC can resemble a thin, scaly patch similar to eczema. About 85% of BCCs show up on the head and neck, though the superficial type more often appears on the trunk and limbs.
BCC grows slowly. It rarely spreads to distant parts of the body, but it can invade surrounding tissue if left untreated. Because of its slow pace, recurrences after treatment sometimes aren’t caught until five or more years later.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) usually appears as a firm, rough, or scaly bump or plaque, sometimes with an open sore in the center. It favors areas that get the most cumulative sun exposure: the backs of the hands, the forearms, and sun-exposed parts of the head and neck. One early form, called Bowen disease, shows up as a slowly growing red, scaly patch. Another variant, keratoacanthoma, grows rapidly and has a hard plug of tissue in its center.
SCC is more aggressive than BCC. It spreads by growing outward into surrounding tissue, and in some cases it can reach lymph nodes or other organs if not treated promptly.
Melanoma
Melanoma accounts for a small fraction of skin cancers, but it is the most dangerous. It originates in the cells that give skin its color, and it is far more likely than BCC or SCC to invade nearby tissues and spread to other parts of the body. Roughly 2.2% of Americans will be diagnosed with melanoma at some point in their lifetime.
What makes melanoma so serious is its ability to metastasize early. A small melanoma on the skin’s surface can send cancer cells into the bloodstream or lymphatic system well before the original spot looks alarming. That’s why early detection matters more with melanoma than with almost any other skin cancer.
How to Spot Melanoma: The ABCDE Rule
Dermatologists use a simple framework to evaluate suspicious moles. Checking your own skin with these five criteria can help you catch melanoma 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 has areas of white, gray, red, pink, or blue.
- Diameter: Most melanomas are larger than 6 millimeters across (about the size of a pencil eraser), though they can start smaller.
- Evolving: The mole has changed in size, shape, or color over the past few weeks or months.
A mole that meets even one of these criteria is worth having a dermatologist examine. A mole that meets several deserves prompt attention.
Rarer Forms of Skin Cancer
Merkel cell carcinoma is a rare but aggressive skin cancer that most often affects people over 50. It typically appears as a painless, fast-growing bump on the face, head, or neck in lighter-skinned people, and more often on the legs in darker-skinned people. The bump may look pink, purple, red-brown, or match the surrounding skin color, and its two sides often don’t match. Because it grows quickly and can spread, early diagnosis is critical.
What Causes Skin Cancer
Ultraviolet radiation is the primary driver. UV light comes in two forms that matter for skin cancer. UVB rays damage skin cell DNA directly and are the main cause of sunburn. They play a direct role in causing melanoma and other skin cancers. UVA rays penetrate deeper into the skin and work alongside UVB to amplify damage. Both types contribute to cancer risk, which is why broad-spectrum sun protection (covering UVA and UVB) matters.
Beyond UV exposure, several factors raise your risk. Your skin’s natural response to sunlight is a major one. The Fitzpatrick scale classifies skin into six types based on how easily it burns and tans:
- Type I: Always burns, never tans
- Type II: Usually burns, minimal tanning
- Type III: Occasionally burns, usually tans uniformly
- Type IV: Rarely burns, always tans well
- Type V: Very rarely burns, tans very easily
- Type VI: Never burns, always tans
People with type I and II skin face the highest risk, but the scale can create a false sense of security for people with darker skin. Skin cancer does occur in types IV through VI. It tends to be diagnosed later in these groups, partly because patients and doctors aren’t looking for it, and partly because lesions can be harder to spot against darker skin.
Other risk factors include a history of blistering sunburns (especially in childhood), frequent tanning bed use, a weakened immune system, a large number of moles, and a family history of melanoma.
How Skin Cancer Is Treated
Treatment depends on the type, size, and location of the cancer. For basal and squamous cell carcinomas caught early, the most common approach is surgical removal. Standard excision involves cutting out the tumor along with a margin of healthy tissue around it, and it cures 93 to 95% of cases.
For cancers in high-risk areas like the face, a technique called Mohs surgery offers better precision. The surgeon removes thin layers of tissue one at a time, examining each under a microscope before deciding whether to take more. This preserves as much healthy skin as possible while achieving a 98% cure rate for basal and squamous cell carcinomas. Recovery from Mohs surgery is typically straightforward, though the procedure itself can take several hours because of the layer-by-layer process.
Melanoma treatment varies widely by stage. Early-stage melanoma confined to the skin is usually treated with surgical excision. More advanced melanoma that has spread may require immunotherapy, targeted therapy, or radiation. The prognosis depends heavily on how early it’s caught, which is why routine skin checks (both self-exams and professional screenings) have such a significant impact on outcomes.
Reducing Your Risk
Sun protection is the single most effective way to lower your risk of all skin cancer types. Sunscreen works by filtering UVB rays before they reach your DNA. The differences between SPF levels are smaller than most people assume: SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97%, and SPF 50 blocks 98%. The jump from SPF 30 to 50 adds just one percentage point of protection, so consistent application and reapplication matter far more than chasing higher SPF numbers.
Sunscreen alone isn’t enough to eliminate risk. Seeking shade during peak UV hours (roughly 10 a.m. to 4 p.m.), wearing protective clothing, and avoiding tanning beds all reduce cumulative UV exposure. Since skin cancer results from DNA damage that accumulates over a lifetime, the habits you build in your twenties and thirties still pay off decades later.