UV radiation and cancer

Ultraviolet (UV) radiation from sunlight is the principal cause of skin cancer, the most common malignancy worldwide. Solar UV radiation is classified as a Group 1 carcinogen by IARC. The three main forms of skin cancer linked to UV exposure are basal cell carcinoma (BCC), squamous cell carcinoma (SCC, also called cutaneous squamous cell carcinoma or cSCC), and melanoma. Incidence of all three is rising globally, with WHO projections indicating continued increases to 2050.

UV radiation is divided into UVA (315-400 nm), UVB (280-315 nm), and UVC (100-280 nm, largely absorbed by the atmosphere). UVB is the most directly mutagenic: it induces the formation of cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts between adjacent pyrimidine bases in DNA. If these lesions are not repaired before cell division, they produce characteristic C-to-T transitions that serve as a UV mutational signature, detectable in SCC and BCC genomes. TP53 mutations carrying this UV signature are present in the vast majority of keratinocyte carcinomas. UVA contributes through generation of reactive oxygen species and indirect DNA oxidative damage, including 8-hydroxydeoxyguanosine adducts. UV radiation also suppresses local cutaneous immune responses, reducing the capacity to recognise and eliminate early malignant cells. In cSCC, the gene PLOD2 has been identified as upregulated in response to chronic UV exposure and contributes to tumour progression through STAT3, ERK, and AKT signalling pathways. UV-induced oxidative stress also remodels membrane lipid composition in melanoma cells, potentially contributing to tumour aggressiveness and treatment resistance.

A review of the evidence on occupational sun exposure and melanoma found consistent associations between intermittent high-intensity UV exposure and melanoma risk, while the relationship between chronic continuous occupational exposure and melanoma is more complex and may involve some protective adaptation in certain populations. A narrative review of photoprotection strategies confirmed that sunscreen use is the best-evidenced intervention for reducing actinic keratoses, keratinocyte carcinomas (BCC and SCC), and potentially melanoma. A university campus intervention campaign to reduce UV exposure improved sun protection knowledge and behaviours among young adults, suggesting educational interventions yield measurable impact. Reviews of skin cancer management found that global incidence of both melanoma and non-melanoma skin cancers has been rising, linked to population-level UV exposure patterns and changes in behaviour including indoor tanning use. Lifestyle medicine analyses confirmed that UV exposure accounts for a substantial proportion of melanoma cases attributable to modifiable behaviours.

People with fair skin, light hair, and light eyes (Fitzpatrick skin types I and II) have the highest risk because reduced melanin content provides less natural UV protection. A personal or family history of melanoma, or the presence of multiple or atypical naevi (moles), significantly elevates individual risk. People who experienced sunburns during childhood or adolescence, or who used indoor tanning devices, face substantially elevated melanoma risk. Outdoor workers with high cumulative UV exposure over working careers face elevated SCC risk. Regional and socioeconomic factors also play a role: populations in tropical and subtropical regions and individuals who cannot access or afford sunscreen face greater UV exposures.

The causal relationship between UV radiation and skin cancer is among the strongest in cancer epidemiology, supported by consistent epidemiological data, laboratory mechanistic evidence including characteristic UV mutational signatures in tumour genomes, and natural experiment data from populations with varying UV exposure. The European Code Against Cancer 5th edition formally classifies solar UV as a Group 1 carcinogen and includes updated UV recommendations. Evidence for the protective effect of sunscreen is strong for SCC and actinic keratoses, and moderate for melanoma.

UV radiation from sunlight is the primary cause of the world's most common cancer type. Evidence strongly indicates that reducing excessive UV exposure, particularly episodes of sunburn, is associated with reduced skin cancer risk. Photoprotection strategies including sunscreen, protective clothing, and shade-seeking are supported by scientific evidence as risk-reduction measures, particularly for fair-skinned individuals and during peak UV hours.