Invisible sunlight. UVB mainly causes sunburn; UVA penetrates deeper and drives photoaging. Both contribute to skin cancer risk.
UVA (315–400 nm)
Longer wavelength; reaches the dermis; associated with photoaging.
UVB (280–315 nm)
Shorter wavelength; primary cause of sunburn; drives vitamin D synthesis.
Evidence & sources
Solar UV radiation is classified as carcinogenic to humans. Evidence: established. Known: IARC Group 1 classification, based on sufficient evidence in humans. Unknown: Individual risk depends on skin type, exposure history and other factors. Source: International Agency for Research on Cancer (WHO), IARC Monographs Volume 100D — Radiation (2012).