Do I Need Sunscreen for Indirect Sunlight?

Direct and diffused sun radiation

When we talk about sunlight, it falls into two categories: direct and diffuse radiation. Direct radiation is pretty self-explanatory – it’s the sunlight that shines directly onto our skin. Diffuse radiation, however, is a bit sneakier. It comes from all directions, not just from above. It bounces off various surfaces including clouds and still manages to reach our skin.

Hats, trees, and other forms of shade can help block direct sunlight, but diffuse radiation often slips past these defenses. This is true for both UVA and UVB rays, so even if you’re in the shade or on a gloomy day, your skin is still getting some damaging UV exposure.

UV exposure on cloudy days

Think you’re safe from UV radiation on a cloudy day? Think again. According to the US National Weather Service, clear skies allow 100% UV transmission, scattered clouds allow 89%, broken clouds allow 73%, and overcast skies allow 31%. Compare this to SPF 30 sunscreen, which only lets 3% of UV radiation reach your skin. Clouds are not effective in blocking much of the UVA rays, so most of these percentages reflect the aging UVA rays. This means that even on cloudy days, your skin is exposed to a good dose of photodamage.  That’s why sunscreen is important, even when the sun is hiding.

False security on cloudy days

Many of us think that if it’s cloudy, hazy, or overcast, we’re naturally protected from the sun. This can lead to skin damage. The truth is, on a hazy day, your skin may get even more UV radiation than on a clear day. This happens because people often skip sun protection when it’s cloudy. You might walk the dog for 15 minutes, spend 15 minutes outside during your commute, go out to grab lunch. Before you know it, you’ve been outside for over an hour without any sun protection.

UV exposure in the shade

As mentioned before, the sun’s radiation can be direct or diffuse. Shade from trees and hats can block direct radiation, but not diffuse radiation. Not all shade is equal when it comes to protecting us from the sun. You could spend hours in the shade and still get lots of sun exposure and risk skin damage – especially if the sun is shining all around your shaded protection.

Hats and umbrellas

Broad-brimmed hats and those with downwards angled brims provide the most UV protection. Research shows that these hats provide an SPF of about 5 for the nose, ears, and neck. Baseball caps offer less protection, especially for the cheeks and chin.

Even large umbrellas can only block so much UV light because of diffuse radiation. The UV light under a small pool umbrella can be anywhere from 17% to 84% of the UV light in direct sunlight (that is, in a best-case scenario, it provides 5 times less protection compared to a broad spectrum sunscreen with SPF 30).

Don’t forget about windows

Let’s talk about indoors. House window glass does offer some protection, blocking about 90% of UV radiation. Car windscreens provide even higher protection. But side windows offer only moderate protection, unless they’re treated with a special film.

Should you use sunscreen indoors then? If your window is getting direct sunlight and you’re spending more than 30 minutes a day near it, it’s probably a good idea to use sunscreen to protect your skin from potential sun damage

So there you have it. Sunscreen isn’t just for beach days or outdoor picnics. Even in indirect sunlight – whether it’s a cloudy day, sitting in the shade, or sitting by a window indoors – our skin is still exposed to UV radiation. The takeaway is this: when it comes to protecting our skin, it’s always better to err on the side of caution. So keep that sunscreen handy and make applying it a daily habit.

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