Skin cancer is caused primarily by ultraviolet (UV) radiation damaging the DNA inside skin cells, triggering mutations that lead to uncontrolled growth. But UV exposure is only the most common cause. Genetics, a weakened immune system, certain chemical exposures, and even viral infections all play a role. An estimated 105,000 new cases of invasive melanoma alone will be diagnosed in the United States in 2025, and non-melanoma skin cancers (basal cell and squamous cell) are so common that most cancer registries don’t even track them.
How UV Radiation Damages Skin Cells
Sunlight contains two types of ultraviolet radiation that harm your skin in different ways. UVB rays (the ones responsible for sunburn) directly damage DNA by fusing neighboring molecules along a DNA strand, creating defects called pyrimidine dimers. These fused segments act like typos in the genetic code. When cells copy their DNA to divide, those typos can become permanent mutations.
UVA rays, which penetrate deeper into the skin and pass through window glass, work through a more indirect route. They generate reactive oxygen species, unstable molecules that attack DNA, proteins, and cell membranes from the inside. Both types of damage can disable tumor-suppressing genes or activate growth-promoting ones, and both contribute to all three major types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma.
Your body has built-in repair systems that catch and fix most of this damage. But with repeated UV exposure over years, some errors slip through. The accumulation of uncorrected mutations is why skin cancer risk rises with age and with total lifetime sun exposure.
Why Childhood Sunburns Matter So Much
Sun damage in early life carries outsized consequences. A meta-analysis pooling data from 27 studies found that people who were sunburned during childhood had a 91% higher risk of developing melanoma later in life, compared to those who weren’t. Sunburns during adolescence increased risk by about 60%, and adult sunburns by roughly 40%. Blistering sunburns in childhood specifically raised melanoma risk by 71%.
The reason childhood burns are so dangerous is that young skin cells are dividing rapidly to support growth. A mutation introduced during this period gets copied into a much larger population of cells over a lifetime, giving it more opportunities to combine with other mutations and eventually trigger cancer.
Indoor Tanning Beds
Tanning beds concentrate UV radiation at intensities that can exceed midday tropical sun. A systematic review by the International Agency for Research on Cancer found that any use of a tanning bed before age 35 is associated with a 75% increase in melanoma risk. The machines emit both UVA and UVB, meaning they cause the same two types of DNA damage as natural sunlight, just in a compressed timeframe.
Skin Tone and Natural Protection
The pigment melanin acts as a natural UV filter, and how much you produce shapes your baseline risk. Dermatologists classify skin into six types based on how it responds to sun exposure:
- Type I: Always burns, never tans
- Type II: Usually burns, tans minimally
- Type III: Burns occasionally, usually tans evenly
- Type IV: Rarely burns, tans easily
- Type V: Very rarely burns, tans very easily
- Type VI: Never burns
The difference in protection is measurable. Deeply pigmented skin filters out about five times as much UV radiation as light skin, providing a natural SPF of roughly 13 compared to about 3 for fair skin. People with Type I and II skin, along with those who have red hair, freckles, or light-colored eyes, face the highest UV-related risk. That said, skin cancer occurs across all skin tones, and it’s often diagnosed later in people with darker skin because both patients and doctors may not expect it.
Inherited Genetic Mutations
About 5% to 10% of all melanoma cases run in families. The most significant inherited mutations involve a gene called CDKN2A, which produces proteins that act as brakes on cell division. When CDKN2A is mutated, those brakes weaken. Germline mutations in this gene are found in 20% to 40% of melanoma-prone families, and the lifetime risk of developing melanoma for carriers varies by geography: roughly 58% in Europe, 76% in the United States, and 91% in Australia by age 80. The higher risk in sunnier climates underscores how genetics and UV exposure compound each other.
Families carrying CDKN2A mutations also face elevated rates of pancreatic cancer, a pattern now recognized as a hereditary cancer syndrome. Other, rarer high-risk gene mutations (in CDK4, BAP1, TERT, and POT1) have been identified in melanoma families as well. Mutations in BAP1 are linked to a broader cancer syndrome that includes a distinctive type of skin mole, eye melanoma, mesothelioma, and kidney cancer.
Beyond these high-risk genes, variants in the MC1R gene (which controls the type of melanin your body produces) act as intermediate risk factors. People with certain MC1R variants tend to produce pheomelanin, a reddish-yellow pigment that provides less UV protection and actually generates damaging reactive oxygen species on its own, even without sun exposure. This means the pigment itself can function as a carcinogen inside melanocytes, the cells that produce it.
Weakened Immune Systems
Your immune system constantly patrols for abnormal cells and destroys many potential cancers before they take hold. When that surveillance system is suppressed, skin cancer risk climbs dramatically. The clearest evidence comes from organ transplant recipients, who take immunosuppressive drugs for life to prevent rejection.
Transplant patients develop squamous cell carcinoma at 65 to 250 times the rate of the general population. Their risk of basal cell carcinoma is about 10 times higher, and melanoma risk is nearly 5 times the norm. Merkel cell carcinoma, a rare and aggressive skin cancer, occurs at 24 times the expected rate. Patients who received heart, lung, or combined kidney-pancreas transplants face two to three times higher risk than kidney-only recipients, because their anti-rejection medications are more potent.
The drugs don’t just suppress the immune system’s ability to find and kill cancerous cells. Some directly interfere with the DNA repair mechanisms that fix UV damage. They also promote the growth of new moles by reducing immune surveillance and increasing the activity of pigment-stimulating receptors in the skin, creating more opportunities for melanoma to develop.
People with HIV, those on long-term immune-suppressing medications for autoimmune diseases, and patients with certain blood cancers also face elevated skin cancer risk for similar reasons.
Chemical and Occupational Exposures
UV radiation gets most of the attention, but several chemical exposures are established skin carcinogens. Arsenic, which can contaminate drinking water in certain regions and is present in some industrial processes, causes a distinct pattern of skin cancers, often appearing as multiple lesions in areas not typically exposed to the sun.
Coal tar and coal-tar pitch, used in roofing, paving, aluminum production, and some industrial coatings, contain carcinogens including benzene. Workers in foundries, coke production, coal gasification, and aluminum smelting face increased skin cancer risk from occupational exposure. Historically, chimney sweeps exposed to soot were among the first recognized occupational cancer cases.
Viral Infections
Certain strains of human papillomavirus (HPV) appear to contribute to squamous cell carcinoma, particularly in people with weakened immune systems. The strains most strongly implicated, HPV 5 and HPV 8, belong to a group called beta-HPV types. These aren’t the same strains linked to cervical cancer or genital warts.
In organ transplant recipients, HPV 5 and 8 are detected at significantly higher rates in squamous cell tumors than in the general population. Renal transplant recipients show antibody levels against HPV 8 nearly three times higher than healthy controls. The virus likely plays a supporting role rather than being the sole cause: it may disable certain tumor-suppressing pathways in skin cells already under stress from UV damage and immune suppression, tipping the balance toward cancer.
Infrared Radiation
Emerging evidence suggests that infrared radiation, the heat-producing portion of sunlight, may play a supporting role in skin cancer development. Infrared light is absorbed by the energy-producing structures inside cells (mitochondria), where it generates a specific type of reactive oxygen species called superoxide. This molecule stabilizes an anti-death protein in cells, making damaged skin cells more likely to survive when they should be self-destructing. In effect, infrared radiation helps UV-damaged cells that would normally be eliminated stick around, accumulate additional mutations, and potentially become cancerous. This is particularly relevant for melanocytes, the pigment-producing cells where melanoma originates.