How the Ozone Layer Is Your First Line of UV Defense
Before any sunscreen touches your skin, a thin band of atmospheric ozone is already filtering the sun's most dangerous rays.
The stratospheric ozone layer, about 15-40 km up, absorbs all incoming UVC and most UVB, while UVA passes through largely unblocked, which is why thinning ozone directly raises ground-level UV and skin cancer risk.
The EPA explains that stratospheric ozone shields the surface from the most harmful UV wavelengths, so any depletion of that layer increases the UV reaching the ground.
Questions we get a lot
How does the ozone layer protect us from UV?
The stratospheric ozone layer, located roughly 15-40 km above the surface, absorbs all incoming UVC and most UVB radiation. This filtering prevents the most damaging wavelengths from reaching the ground. UVA, however, passes through the ozone layer largely unblocked.
Why does a thinning ozone layer increase skin cancer risk?
When the ozone layer thins, it absorbs less UVB, so more of that harmful radiation reaches ground level. Higher UVB exposure raises the risk of sunburn and skin cancer. The EPA notes this direct link between ozone depletion and increased surface UV, which is why personal sun protection remains essential.
r/askscience: 'If the ozone layer blocks UV, why do we still need sunscreen at all?'