YES, UVA rays do enter through the window: and 6 myths about sunlight

Just saving this right here for the next time someone decides to explain sunlight to me.

Source of the screengrab:

You would think the sun was invented in Spain. They’re so proud of it being so abundant and almost take it personally that I’m photosensitive.

I get migraines and tiny blisters from the sun. When I ride in cars on a bright day I might wear a hat as well as sunglasses.

Invariably, someone has to “explain” to me that the sun doesn’t enter through the glass and imply I’m being dramatic by ((checks notes))…minding my own business and not wanting to puke and burn?

While I’m here, I might as well save future-me time and drop some other myth-busting about the sun I regularly have to do..

1. UVB doesn’t enter through glass (mostly)

I have a parrot. Parrots need UVB for their feathers. Most windows block UVB. And it’s not like I have any way of knowing what glass in is this flat, so I have a UVB lamp on top of my bird’s cage. Once again, I find that someone in the room will always feel like they need to explain their invention to me.

2. Vitamin D needs UVB

Lord, I – a person who spent 3 years reciting metabolic pathways forwards and backwards for my biochemistry degree- had a woman with zero qualifications other than two kids explain that I didn’t know how vitamin D was formed (I studied it from its synthesis from cholesterol, thanks!) and that my baby didn’t need the vitamin D drops prescribed by the pediatrician because she could get it from the glass window.

“Virtually all commercial and automobile glass blocks UVB rays. As a result, you will not be able to increase your vitamin D levels by sitting in front of a sunny window, though much of the UVA radiation will penetrate the glass and may be harmful.”

Does Sunlight Through Glass Provide Vitamin D? New York Times ask well

Small babies cannot be exposed to direct sunlight. Glass doesn’t let enough UVB through. So they need drops.

3. You don’t need sun exposure every day to get vitamin D.

“Exposure of the hands, face and arms two to three times a week is sufficient to meet the daily body vitamin D requirements in most individuals during the spring, summer and fall”

Treatment of vitamin D deficiency with UV light in patients with malabsorption syndromes: a case series

Although you can go out if you want to, though.

4. Grey skies or clouds don’t block UV rays

Thanks to public ad campaigns from either our governments or skin cancer charities, most people in the UK and Australia know this one. I have to remind my husband of this regularly.

What’s happening is he’s assuming that infrared levels and UV levels are always equal. They’re not.

On a grey and cloudy day, the infrared rays of the sun – the part that makes our skin feel hot- are filtered much more than the UV rays – the part that ages us and burns- are.

Without that heat, we can forget we’re still being exposed all day and rack up skin damage.

“The US National Weather Service’s calculation of the UV index assumes that clear skies allow virtually 100% of UV transmission, scattered clouds 89%, broken clouds 73%, and overcast skies 31%.”

Can I get a sunburn on a cloudy day? Clear dermatology

This also applies to sunny days with cool wind, or being in a nice cool pool.

Don’t make the mistake of assuming skin heat= skin damage.

5. Shade is for onioning, not a standalone SPF

That shadow under the tree looks so dark and inviting. It must surely be blocking enough of the sun to mean no SPF or hat is needed, right?

That shade only looks dark in the way that going indoors feels really dark coming straight from the sun. Our eyes are just adjusted to the bright light.

“Single trees provide a Sun Protection Factor (SPF) from 4 to >50, depending on the foliage density and proximity to the shadow perimeter.”

How protected am I in the shade or under an umbrella? Clear dermatology

An SPF of anywhere between 4 to under 50 doesn’t sound reliable to me.

Shade is good for onioning spf protecion layers, through. Wear your hat and your SPF and seek shade between 12-3.

6. Plants use photons, not UV rays to grow.

It’s hard being a STEM girl in a social sciences world.

Occasionally as a gotcha, someone will point to my plants indoors and say, “if UVB is blocked then how do they grow!?”

I’m so glad you asked because otherwise sitting exams in photosynthesis no less 3 separate times in my academic life would have been a waste.

Sunlight has dual properties. It can be represented as waves – such as UVA and UVB and ultraviolet waves – but it also has the properties of a particle. We call this particle propety “photon”.

It’s the “photon” property that plants use to photosynthesize and grow.

Plants don’t use UV rays to grow (maybe some specialist species do), but do need red and blue light– in nature this light comes from the colours of dawn and dusk and that lovely blue hour that follows sunset and precedes the dawn.

That’s why you can buy LED red and blue lights for plants pretty cheap. They’re not high-tech.

While I wrote this mostly to save myself energy in the future, I hope that arms you with facts (and sunscreen) in case you’ve heard different things about when to slather up or not.

signed, the healing mom
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