Yes, You Can Burn on a Cloudy Day: The 80% UV Rule
Gray skies feel safe, but most of the sun's UV slips right through the clouds and onto your skin.
According to the World Health Organization, up to 80 percent of solar UV radiation can penetrate light cloud cover, which means overcast skies are not protective against sunburn or long-term skin damage.
The World Health Organization stresses that cloud cover gives a false sense of security because UV radiation, not brightness or heat, drives skin damage, and a large share of UV reaches the ground even when the sky looks gray.
Questions we get a lot
How much UV gets through clouds?
The World Health Organization states that up to 80 percent of solar UV radiation can penetrate light cloud cover. That's why a hazy or overcast day can still cause sunburn even though it feels cooler and dimmer. The protection clouds offer against UV is far weaker than most people assume.
If it's cool and gray, why do I still need sunscreen?
Sunburn is caused by ultraviolet radiation, not by heat or how bright the sky looks. The WHO notes that UV can pass through cloud cover in large amounts, so a cool, overcast day can still deliver a damaging dose. Wearing sunscreen on gray days is a sensible default rather than overkill.
How do I know when UV is high if I can't see the sun?
Check the UV index rather than judging by appearance, since the WHO highlights that UV levels are not reliably indicated by warmth or visible sunlight. Many weather apps report the UV index alongside temperature. When it reaches moderate levels or higher, sun protection is advisable regardless of cloud cover.
r/SkincareAddiction: 'It was completely overcast all day and I still came back pink, how is that even possible if the sun was never out?'