Do You Need Sunscreen on a Cloudy Day? (Up to 80% of UV Gets Through)
The sky is flat grey, the sun is nowhere in sight, and skipping sunscreen feels like the obvious call. It isn’t. Clouds block a lot less UV than they look like they should, and the ray that ages your skin barely notices them. The real question is whether you need a cloudy day sunscreen at all, what actually gets through an overcast sky, and the one twist that catches almost everyone out, with the science from the American Academy of Dermatology, the World Health Organization, and the EPA.
TL;DR: Yes, you still need sunscreen on a cloudy day. Dermatologists put it plainly: even on cloudy days, up to 80% of the sun’s harmful UV rays can get through the clouds. UVA, the wavelength that ages skin, passes through cloud and even window glass, so it reaches you whatever the forecast says. Thin cloud can also scatter UV and sometimes push it above a clear-sky level. The fix is the same as any other day: a broad-spectrum SPF 30 or higher every morning, in the amount the label assumes.
Do you need sunscreen on a cloudy day?
Short answer: yes. The American Academy of Dermatology states that even on cloudy days, up to 80 percent of the sun’s harmful UV rays can penetrate the clouds [1]. Read that number again. A sky that looks like it has switched the sun off is still letting through most of the radiation that burns and ages your skin. The overcast look is a trick of visible light, and visible light is not what damages you.
This is why grey days quietly rack up sun damage that nobody credits to the weather. You feel protected, so you go longer without cover, and the UV keeps working right through it.
Clouds dim the light, not most of the UV
The gap that fools people is the gap between brightness and UV. Clouds are very good at scattering visible light, so the day looks dim and feels cool. They’re much worse at stopping ultraviolet. The EPA says it in one line: even on a cloudy day, you can be sunburned by UV radiation [3]. Sunburn is the visible proof that UVB got through. The damage you can’t see, from UVA, is happening alongside it.
So the mental shortcut of “it’s not bright, so I’m fine” fails at the physics. Your eyes are reading brightness. Your skin is being dosed by a different part of the spectrum that the clouds let pass.
UVA is the ray that ignores the weather
Here is the part that makes a cloudy day sunscreen non-negotiable. There are two kinds of UV that reach the ground. UVB is the one that burns, and it does drop somewhat under heavy cloud. UVA is the one that ages skin, and it’s far more stubborn. The AAD notes that UVA rays, the aging rays, can prematurely age your skin with wrinkles and age spots, and can pass through window glass [1]. A ray that goes through glass is not going to be stopped by a layer of cloud.
That steady, year-round UVA is the same reason we tell people to wear sunscreen at a desk by a window and behind the wheel, which we cover in our sunscreen-for-driving piece. This is the reason daily use beats seasonal use, a point we make in our complete Korean sunscreen guide. Cloud cover changes how the day looks. It barely changes the UVA reaching your face.
The twist: thin cloud can push UV higher
This is the detail almost nobody knows, and it turns the myth on its head. You would assume any cloud lowers your UV. Usually it does. But the World Health Organization warns not to underestimate the UV passing through clouds, and adds that light or thin clouds have little effect and may even enhance UV levels because of scattering [2]. In other words, a patchy or hazy sky can bounce extra UV down at you, so your reading can sit above what a clear sky would have given.
So a cloudy day is not a reliable day off. Heavy, dark storm cloud does cut UV a lot. The bright-grey and patchy skies that make up most “cloudy” days are exactly the ones that let plenty through, and occasionally more.
Your cloudy day sunscreen routine
The routine doesn’t change for grey weather. It’s the same broad-spectrum habit, applied like you mean it:
- Wear it every morning, SPF 30 or higher. Broad-spectrum covers both UVA and UVB. Make it part of getting dressed, not a decision you make by looking out the window, because the window is the thing that lies to you.
- Use enough. Skimp on the layer and you get only a fraction of the SPF on the label. Aim for about a teaspoon for the face and neck, which we break down in our how-much-sunscreen guide. Under-applying on a cloudy day is a double hit.
- Reapply if you are out for hours. Every two hours outdoors, cloudy or not. The morning layer fades whether or not the sun is visible.
- Don’t wait for the UV index to look scary. A moderate index on an overcast day is still enough for daily damage to add up over months and years.
The takeaway is short. The forecast is about rain, not radiation. Treat sunscreen as a daily thing you do regardless of the sky, and the cloudy-day question answers itself.
FAQ
Do you need sunscreen on a cloudy day?
Yes. The American Academy of Dermatology says up to 80 percent of the sun’s harmful UV rays can penetrate the clouds, so a grey sky is not real protection. UVA in particular passes through cloud and glass, so it reaches your skin whatever the weather looks like.
How much UV gets through the clouds?
According to the American Academy of Dermatology, even on cloudy days, up to 80 percent of the sun’s harmful UV rays can penetrate the clouds. Clouds scatter visible light, which makes the day look dim, but they are far worse at blocking ultraviolet.
Can you get sunburned on a cloudy day?
Yes. The EPA states that even on a cloudy day, you can be sunburned by UV radiation. Sunburn is the visible sign that UVB got through, and the UVA that ages skin is passing through the cloud at the same time.
Is UV always lower when it’s cloudy?
No. Heavy, dark cloud does cut UV a lot, but the World Health Organization notes that light or thin clouds have little effect and may even enhance UV levels because of scattering. A hazy or patchy sky can send more UV your way, not less.
Sources
The science and guidance:
[1] American Academy of Dermatology, Sunscreen FAQs (even on cloudy days, up to 80% of the sun’s harmful UV rays can penetrate the clouds; UVA rays can prematurely age your skin and can pass through window glass): link
[2] World Health Organization, Radiation: Ultraviolet (UV) radiation, Q&A (be careful not to underestimate the amount of UV radiation passing through clouds; light or thin clouds have little effect and may even enhance UV levels because of scattering): link
[3] US EPA, Ultraviolet (UV) Radiation and Sun Exposure (even on a cloudy day, you can be sunburned by UV radiation): link
