Do Hats and Umbrellas Protect Well From the Sun? (with video)

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Instead of talking about sunscreen like I usually do, we’re going to dive into some of the things you can use to protect your skin apart from sunscreen (I can feel my sunscreen propaganda shillbucks slipping away right now).

As much as we all love sunscreens, they are a bit of a pain in the butt. You have to apply them right, you have to apply enough, they can sometimes give you clogged pores and rashes, they rub off, they can be uncomfortable…

So it seems like there has to be a better option, right?

Well, sometimes there is!

Today’s topic is hats, umbrellas and shade in general: how much protection they give, what to look for, and whether you can use them instead of sunscreen.

The video is here, keep scrolling for the text version…

Swiss cheese and sun protection

I think most of us have seen this Swiss cheese diagram, with respect to protecting ourselves from COVID-19:

Credit: Ian M Mackay

This is a model used in risk analysis. The idea is that although each layer of protection has shortcomings, enough layers of imperfect protection will give you pretty decent protection overall.

And this is how we should think about sun protection too – sunscreen is an important layer, but it’s not the only layer. In Australia, we have the slogan Slip Slop Slap Seek Slide: Slip on a shirt, slop on sunscreen, slap on a hat, seek shade, and slide on sunglasses.

sun-protection-swiss-cheese

But how well do each of these work? Why do we still get burnt in the shade? Can you just wear a hat instead of sunscreen?

UV exposure

Let’s start by talking about where UV comes from. It’s the sun, obviously! But there are two types of UV exposure, which you might remember from my post about whether or not you need to wear sunscreen indoors.

Related post: Should You Wear Sunscreen Indoors? The Science (with video)

Direct UV exposure is when the sun is directly shining on you. When you’re in full sun you’re getting direct exposure, but when you’re in the shade you have no direct exposure.

Direct UV: sun vs shade

The other type is indirect or diffuse UV exposure. Basically, the sun’s UV bounces off something else onto you. The “something else” is mostly air molecules up in the sky, but UV can also be reflected by other objects onto you.

direct vs diffuse UV

Diffusion also happens with visible light, and it’s why you can still see things that are in the shade. Shorter wavelengths get diffused more, so there’s more diffuse UV around than diffuse visible light, and more diffuse UVB than UVA.

If you’re standing in the middle of a field, you’re getting 60% diffuse UV and 40% direct UV as a very rough estimate.

pie chart UV direct diffuse

The actual percentages change with lots of factors such as how high the sun is in the sky, the wavelength of UV you’re talking about, and where you are in the world. The key takeaway is that UV shining directly on you is often less than half of the UV you could be getting.

How much UV?

Working out how much direct UV you’re getting is straightforward: if there’s sun shining directly on you, you’re getting that 40% direct UV exposure.

Working out diffuse UV is trickier – we need to think about what’s bouncing UV onto us.

Diffuse UV and Sky View

If you’re outside, the main thing diffusing UV onto you is probably the sky. We can use something called Sky View to estimate how much UV is bounced off the sky.

If you’re standing in the middle of a field, you’re exposed to the inside of a continuous dome of sky. That’s 100% sky view, which translates to 100% exposure to diffuse UV.

100 sky view

The amount of diffuse UV you get is proportional to the amount of sky you can see, so if there’s stuff blocking your view of the sky, then you get less sky view and lower diffuse UV.

If 50% of the sky is blocked out, then you end up with around half the diffuse UV:

50 sky view

Let’s combine this with our estimates of direct UV. 

If you’re in direct sun and half the sky is blocked by, say, a barn, then you’re getting around 40% direct UV plus half of 60% diffuse UV (30%). 40 + 30 = 70%, so you’re getting 70% of the UV you’d get standing in the middle of a field.

50 sky view direct sun

pie chart 70 UV

Let’s say the sun moves behind the barn, so you’re now fully in the shade but half the sky is still blocked. Then you’re getting none of the 40% direct UV, but you’re still getting half of the 60% diffuse UV. This leaves you with somewhere around 30% of the UV compared to being in the middle of a field with 100% sky view.

50 sky view no direct sun

pie chart 30 UV

When the ground betrays you

In some situations, the ground can also reflect a significant amount of UV. Here’s a table of the UV reflected by some different surfaces (extracted from here):

ground albedo UV

Most surfaces absorb most of the incoming UV and won’t reflect much. Grass, dirt, asphalt (bitumen), wooden boards, most types of concrete reflect less than 10% of UV, so the ground ends up contributing less than 5% of your total UV exposure.

However, a few types of surfaces can reflect more. In particular, some countries apparently have tiny chunks of ice that fall from the sky sometimes – I’ve been told this is called “snow”, and this can reflect up to 90% of the incoming UV. This can mean you get up to the same amount of UV from the ground as from the sun and the sky combined

Choppy surf and metal surfaces can reflect 25%, while some types of sand can reflect up to 40% (although most sand has low reflection).

So depending on the UV index that day, the contribution of diffuse UV from the ground when you’re standing in the shade could still be quite high.

Burning in the shade

So the contributions from the sky and the ground is why it’s still possible to get burned when you’re entirely in the shade.

If you’re facing the sky, or a ground surface that’s bouncing direct UV towards you, you can still be getting a lot of UV – especially those short wavelengths of UVB that get scattered really well and cause burning.

And it’s a bit deceiving, because when you’re in the shade you’ll feel cooler, even if you’re getting a lot of UV. UV doesn’t produce a lot of perceptible heat. It’s visible light and IR from the sun that make you hot, and they make up over 90% of the energy from the sun even though the rays don’t bounce around as much as UV. If you face away from the sky while you’re in the shade, you’ll cut down the UV exposure on your face by a lot, even though you’ll probably feel pretty similar temperature-wise.

Hats

So with all this background, we can work out how much UV protection hats provide.

Material

Hats are usually made with thick material that blocks out almost all the direct UV. For example, an Akubra hat will only let in 0.05% of direct UV (1/2000th of the incoming UV). 

akubra hat
Probably the national hat of Australia

Of course, if you have a hat made out of thinner material like fabric, then it’ll be different. The factors discussed in my post on UV protective clothing apply here as well.

Related post: How to Choose UV Protective Clothing (with video)

For a hat that blocks out more UV, your best bet is:

  • synthetic fabric
  • tightly woven with as few and small holes as possible
  • thicker fabric / multiple layers
  • intense colours (dyes can absorb UV)

A UPF rating will mean you don’t need to guess.

Size and shape

Unsurprisingly, the bigger the hat, the more sky it’s going to block out and the more diffuse UV you’ll be protected against.

The angle of the hat brim will also make a difference – the same size hat with the brim turned down blocks out more sky and more diffuse UV.

Facial regions

Different parts of the face will also get different protection. For a cap, if we think about sky view, a tiny person standing in the middle of your face won’t see as much sky and will get less UV, but a tiny person standing on your cheek sees almost all the sky and gets all the diffuse UV (plus they’ll get direct UV some of the time).

But even with a broad brimmed hat there can be a big difference. The further up towards the hat, the higher the protection since the tiny person sees less sky. This means the forehead and nose get more protection, while cheeks and chin get less.

Hats also block more UV for parts of your face that are angled upwards compared to parts angled sideways – a little dude lying on your nose is going to see less sky than a little dude leaning against your cheek.

Ground contribution

Hats obviously can’t protect you from any UV bouncing from below, which could be a significant problem if you’re on a very reflective surface like snow (with common hat designs, anyway).

Overall UV reduction in practice

As an illustration, one study estimated the annual UV reduction when an outdoor farm worker in Queensland wore a broad brimmed Akubra Drover with only 0.05% UV transmittance all year round. Forehead UV exposure was reduced to about one-seventh, while nose UV dropped to one-third. However, cheek exposure dropped by less than half.

The overall facial UV exposure reduced by an average of 2-6, but up to 100 times in some facial regions.

Umbrellas

Size and distance

We can think about handheld umbrellas much like we thought about hats.

Umbrellas are larger and further away from your head. The further away it is, the bigger it has to be to block out the same amount of sky. If the umbrella doubles in distance away from, say, your nose, then the radius has to double to give the same protection.

Material

One big difference between umbrellas and hats is that umbrellas tend to be made of thinner material, so more direct UV can get through.

The actual UV transmission is really variable between different umbrellas. In studies, regular rain umbrellas can let through as much as 23% of UV, or as little as 0.1%. Unsurprisingly, given what we know about UPF clothing, black umbrellas and UPF-rated umbrellas block more UV. 

Position

Another difference between hats and umbrellas is that you’re usually off to the side with an umbrella. Depending on the size of the umbrella, how far above your head it is and how you hold it, the umbrella can end up giving you worse protection on one side of your face than a hat would (but on the flip side, you won’t get hat hair). 

Overall UV reduction in practice

Annoyingly, most studies on umbrellas are with beach umbrellas that are stuck into the ground and much bigger than a handheld umbrella. 

One study estimated that beach umbrellas can give a protection factor of 3-17 depending on the size of the umbrella, where you are relative to the umbrella, where the sun is and so on.

Another study estimated that If you’re sitting in the shade of an umbrella in summer in the middle of the day with no other protection, you could still burn in 2 hours.

Takeaways

Hats and umbrellas are great for giving UV protection that you don’t need to reapply, and won’t wear off quickly. They also protect areas where you might not be able to get to with sunscreen or clothing, like your scalp and the edge of your eyelids (although there are sunglasses, but that’s going to be a separate post).

They’re particularly good for protecting against direct UV, but that 60% diffuse UV from the sky is what gets you – they’re usually good at blocking the circle of sky right above your head, but UV is coming in all around.

To protect against diffuse UV, you’re going to need “sideways” protection that gets between your skin and the sky. Walls and trees can be helpful depending on location. For more portable protection, sunscreen and clothing will be more suitable.

If you’re in a high sun exposure situation, then remember the Swiss cheese layers and use multiple types of sun protection rather than just relying on one type. High sun exposure includes the obvious situations like going to the beach and exercising in the sun, but also when you’re at the snow since the ground reflects a lot of UV.

In lower UV exposure situations, like if you’re only going outside for a few minutes or in the middle of winter (assuming you’re not in this mythical snow), you can get away with less layers of Swiss cheese.

References and Further Reading

Wong JC et al., Annual reduction of solar UV exposure to the facial area of outdoor workers in Southeast Queensland by wearing a hat, Photodermatol Photoimmunol Photomed. 1996, 12, 131-135. DOI: 10.1111/j.1600-0781.1996.tb00189.x

Backes C et al., Facial exposure to ultraviolet radiation: Predicted sun protection effectiveness of various hat stylesPhotodermatol Photoimmunol Photomed 2018, 34, 330-337. DOI: 10.1111/phpp.12388

Turner J, Parisi AV, Ultraviolet radiation albedo and reflectance in review: the influence to ultraviolet exposure in occupational settings (open access), Int J Environ Res Public Health 2018, 15, 1507. DOI: 10.3390/ijerph15071507

Religi A, Ground UV irradiance and 3D rendering techniques to predict anatomical solar UV exposure in skin cancer research and prevention (open access), Université de Genève PhD Thesis 2018. DOI: 10.13097/archive-ouverte/unige:112464

McMichael JR et al., UV radiation protection by handheld umbrellas (open access)JAMA Dermatol 2013, 149, 757-758. DOI: 10.1001/jamadermatol.2013.2519

Utrillas MP et al., Ultraviolet radiation protection by a beach umbrellaPhotochem Photobiol 201086, 449-456. DOI: 10.1111/j.1751-1097.2009.00677.x

Ou-Yang H et al., Sun protection by beach umbrella vs sunscreen with a high sun protection factor: a randomized clinical trial (open access), JAMA Dermatol. 2017, 153, 304-308. DOI: 10.1001/jamadermatol.2016.4922

Ou-Yang H et al., Sun protection by umbrellas and wallsPhotochem Photobiol Sci. 2017, 16, 1537-1545. DOI: 10.1039/c7pp00214a

Religi A et al., Body Anatomical UV Protection Predicted by Shade Structures: A Modeling StudyPhotochem Photobiol. 2018, 94, 1289-1296. DOI: 10.1111/php.12949

More on sky view in my analysis of wearing sunscreen indoors

Skincare Guide


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9 thoughts on “Do Hats and Umbrellas Protect Well From the Sun? (with video)”

  1. I love your posts! Just finished reading your latest one on direct and indirect uv exposure. Your chart on how much exposure you get from below did not list swimming pools or oceans. I am an esthetician in Florida and my clients always say, “but I wear a hat in the pool (or ocean)”. I’d love to have a comeback for that!

    Reply
  2. Michelle,
    Thank you for this article. I’m a sun-exposure boffin(!) of 35 years (Australian) and an almost-daily UV chart watcher, but I’m ambivalent to sunscreen, and inconsistent. I suspect this comes from being led to think simple zinc-based ones were ‘better’ – but they’re very drying and uncomfy for me, so then I’d avoid using any product. (Now I’ll broaden my search a bit – Ultra Violette next?- thank you for your reviews).
    But I’m very into hats, clothes, high UV-times avoidance (umbrellas when I’m feeling un-self-conscious), so it’s always great to learn more about these modes of protection. I find they’re less disruptive to use, knowing that sunscreen takes time (20 min?) to activate, and I’m only going outside (in decreasing UV) for 20 min. That said, I’m aware that even low UV exposure is cumulative so I’m not sure I want to see what my lifetime sun-damage photo would look like. Or is that a gimmick?
    Thanks again,
    Cass

    Reply
  3. I just did my own totally anecdotal diffuse UV light research and found that in the week that I was spending my days Stand Up Paddle Boarding on the sea, I gained more color on my face than in the week I spend doing the grape harvest – wearing the same hat and same SPF. Sand and sea are really diffusing the UV light very well!
    Of course I did not factor in the amount of times I actually fell off the board, probably loosing quite some sun protection through that…
    I guess my study is flawed not only by the low number of participants!

    Reply
  4. I can’t tell you how excited I am to have my work cited by a sunscreen propagandist ;-). Mine is the albedo and reflectance review, which of course I am inordinately proud. That review is a partial summary of my PhD so having it out in the world means folks like you can access it and use it for good!

    I like how you spent time explaining the how sky view and UPF (and they work only depending on how you use the thing). Keep it up I really enjoy and appreciate the work you do in your blog and videos!

    Reply
    • That’s so cool! Very honoured to have you comment on my blog, it was a very very useful paper and I’m so glad you made it open access! ^_^

      Reply

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