UV radiation and skin cancer
Ultraviolet radiation; UVR; UVA; UVB; sunlight and skin cancer
Ultraviolet radiation from natural sunlight and artificial sources is classified by the WHO/IARC as a Group 1 carcinogen — sufficient evidence for carcinogenicity in humans. UVA (315–400 nm) penetrates deeply and is the principal driver of photoageing, immunosuppression and BCC; UVB (280–315 nm) drives most direct DNA damage (cyclobutane pyrimidine dimers), erythema and cSCC. Melanoma risk is driven principally by intermittent intense exposure and childhood sunburn; cSCC by cumulative lifetime exposure; BCC by both. Understanding UV biology underpins photoprotection, sunbed counselling and the management of immunosuppressed patients.
UVA vs UVB — biology
- UVB (280–315 nm) — absorbed by stratum corneum and upper epidermis; principal cause of erythema (sunburn), direct DNA damage (cyclobutane pyrimidine dimers, 6-4 photoproducts), p53 mutations and squamous-cell carcinoma initiation. Variable across seasons and time of day.
- UVA (315–400 nm) — penetrates dermis; predominantly indirect oxidative damage via reactive oxygen species. Drives photoageing, immunosuppression, melanoma initiation, basal-cell carcinoma. Far more abundant than UVB and present at high levels year-round, including through window glass and on cloudy days.
- UVC (100–280 nm) — almost entirely absorbed by the ozone layer; not relevant to natural exposure.
UV and cancer types
- cSCC — cumulative lifetime UV dose drives risk; chronic sun-exposed sites (head, neck, forearms, dorsal hands).
- BCC — both intermittent intense and cumulative exposure; site-related (head and neck dominant).
- Melanoma — intermittent intense exposure, sunburn in childhood and adolescence are dominant; truncal lesions in men, lower-limb in women.
- Merkel cell carcinoma — chronic UV-damaged skin + MCPyV interaction.
- Lentigo maligna / actinic keratoses — chronic cumulative damage.
UV-induced immunosuppression
- UV exposure suppresses cutaneous and systemic immunity through Langerhans-cell depletion, regulatory T-cell induction and cytokine modulation.
- Contributes to skin cancer development and may impair tumour immune surveillance.
- Particularly relevant to organ transplant recipients who are already pharmacologically immunosuppressed — UV protection in OTRs reduces non-melanoma skin cancer incidence substantially.
UV index and UK exposure
- UV Index (UVI) — open-ended scale; UK summer typically peaks at 6–8 (high).
- UVI ≥ 3 — sunscreen recommended; UVI ≥ 6 — additional protection (shade, clothing, hat).
- UV does not need to feel hot to cause damage — overcast days can deliver up to 80% of clear-day UV.
- Snow, sand and water reflect UV — exposure is intensified.
- UK Met Office and many weather apps provide daily UVI forecasts.
IARC classification and policy
- UV radiation is an IARC Group 1 carcinogen — same category as tobacco, asbestos, ionising radiation.
- Solar radiation, broad-spectrum UV, sunbeds — all Group 1.
- UK policy — Sunbeds (Regulation) Act 2010 (under-18s banned); ongoing campaigns on photoprotection.
References
- IARC Monograph 100D. Radiation — UV (solar and equipment). 2012.
- WHO. Ultraviolet radiation and human health. Fact sheet; 2017.
- Public Health England / UK Health Security Agency. UV index and health information. GOV.UK; accessed 18 May 2026.
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