Monday, January 19, 2026

I had it wrong it isn't the infrared that makes it through the Clouds it's the ultraviolet rays (UV)

 Question why it is you can get skin cancer more easily on a cloudy day than a day of full sun?

begin answer quote: 

You can get skin cancer more easily on a cloudy day because
clouds don't block all UV rays, with up to 80% still reaching your skin, and the lack of intense heat makes you less likely to apply sunscreen, leading to prolonged, unnoticed damage from UVA and UVB rays that cause skin cancer. Some clouds, like cirrus, can even scatter UV light, potentially increasing your exposure, while UVA rays, a major skin cancer contributor, are minimally affected by cloud cover. 
Why cloudy days are still risky:
  • UV Penetration: Clouds are poor blockers of UV radiation, allowing a significant amount (up to 80%) to pass through to the surface.
  • Less Perceived Heat: Clouds block infrared (heat) radiation more effectively than UV, so it feels cooler, tricking you into thinking the sun isn't strong, but UV rays are still active.
  • UVA Rays Persist: UVA rays, which penetrate deeper and contribute significantly to aging and cancer, are present throughout the day and aren't significantly reduced by clouds.
  • Reflection: UV rays can bounce off surfaces like water, sand, and concrete, increasing your total exposure.
  • Cloud Type Variation: Certain thin clouds (like cirrus) can actually scatter and intensify UV rays, increasing risk. 

How to protect yourself:
  • Apply Sunscreen: Use broad-spectrum SPF 30 or higher on all exposed skin, even when it's overcast.
  • Wear Protective Clothing: Hats, sunglasses, and UPF-rated clothing offer physical barriers.
  • Seek Shade: Avoid peak sun hours (10 a.m. to 4 p.m.). 

  • VERIFY: Certain clouds can create higher UV ray levels
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  • Can You Get a Sunburn on a Cloudy Day? - Dignity Health
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