95% of the UV Hitting You Is UVA — The Aging Ray You Forget
UVB gets the sunburn headlines, but the UV that reaches you all day is overwhelmingly UVA — the wavelength that quietly drives photoaging.
The UV that reaches Earth's surface at midday is roughly 95% UVA and only 5% UVB; UVC and most UVB are filtered out by stratospheric ozone, which is why year-round UVA exposure is a major driver of photoaging.
International health bodies note that because UVA makes up the large majority of ground-level UV and penetrates the skin more deeply, it is a significant contributor to long-term skin aging and damage.
Questions we get a lot
What percentage of UV is UVA?
About 95% of the UV that reaches Earth's surface is UVA, with only roughly 5% UVB. UVC and most UVB are absorbed by stratospheric ozone before reaching the ground. Because UVA dominates and penetrates deeply, it is a major driver of photoaging.
Why does UVA matter if UVB causes sunburn?
UVB causes most sunburn, but UVA penetrates deeper into the skin and is a key driver of photoaging and wrinkles. It is also present year-round, even on cloudy days and through glass. That is why broad-spectrum protection, which covers both rays, is recommended rather than focusing on SPF alone.
r/SkincareAddiction: 'If UVA is most of the UV outside, why do so many products only seem to brag about their SPF number?'