National Sun Screen Day 27th May

By Ruth Perkins

Zaraultz

Sunny days ahead! (All rights reserved)

Well hello sunshine! Today is National Sun Screen Day so let’s take a look at our skin’s love/hate relationship with that great glowing sphere in the sky.

As well as all the light we can see, there is an awful lot of light emitted from the sun that we can’t see. Some of that invisible light is dangerous for us, but lots of it is blocked by our wonderful atmosphere.

Ultraviolet (UV) light is what tans and burns our skin. UV is part of the electromagnetic spectrum. Most scientists group ultraviolet light is into 3 different types (scientists studying things in space use other terms).

  • UVA can penetrate deep into our skin giving us an immediate tanning effect and contributes to skin ageing and wrinkles. 95% of the UV that reaches us is this type.
  • UVB can only effect the top skin layers, but is responsible for delayed tanning and burning, skin ageing, and increases the chance of skin cancer.
  • UVC is the most damaging, but filtered by our atmosphere. The hole in our ozone layer allows some of the through so more research is being done into protecting ourselves from it.

Recent research has found a delayed damaging effect caused by both UVA and UVB which could lead us to a need for new after exposure products.

How can we protect ourselves from the harmful effects of UV?

One tool is to keep an eye on the UV Index (measurement of UV intensity) for where you live and looking at the guidelines, which cover how often you need to apply sunscreen to avoid burning. The sun is at it’s most intense between 10am and 4pm, when it is highest in the sky.

Clothing that includes long sleeves and trousers will protect your skin. Sun glasses with UV filters and wide brimmed sun hats are a great way to protect your eyes – around half of the UV damage to your eyes happens before you are 18.

The idea that you can build up resistance to burning with a “base tan” has been recently disproved. Some people take ultraviolet protection to the extremes with face-kinis. Is this what we should all be wearing? No!

I don't go any where without my sunglasses!

I don’t go any where without my sunglasses! (All rights reserved)

Before you go and buy a face-kini… some sun is good!

What does our skin love about sun exposure? Ultraviolet light absorbed by the skin is the main way we produce vitamin D. (So technically it’s a hormone not a vitamin because we can make it, but it was named a while ago before we fully understood that!).

In the UK we can only make vitamin D from sun exposure between April-October. This is because of our latitude and the earth’s tilt. During summer our part of the world tilts closer to the sun giving us longer days, and more intense sunlight as it travels though less of our protective atmosphere when higher overhead.

10-15 minutes in the sun without sunscreen between 11am-3pm, with 20% of our body uncovered (e.g. arms and face) is adequate for most people in the UK to get sufficient vitamin D. The paler your skin, the less time in the sun you need. Also if you double the amount of skin exposed e.g. arms and legs you can halve the time required. Basically the bottom line is it is far far less time needed to get vitamin D than the time it takes to burn. As sunburn is a risk factor for skin cancer you need to avoid that at all costs.

There are some great online calculators to help you calculate the amount of time required based on latitude, time of year, weather, skin colour etc. The Norwegian Institute for Air Research has a pretty thorough vitamin D calculator.

What happens when we aren’t exposed to the sun?

So what about in the winter? If you have built up your stores over the summer you will have enough to last six months, but you can also get vitamin D from food. In the UK we get about 10-20% this way. Oily fish is a good source, and a lot of cereals and margarines are fortified. Surprisingly if you leave mushrooms out in the sun for an hour they absorb the ultraviolet light and make Vitamin D which we can then eat.

Backlit Mushroom

A source of vitamin D? “Backlit mushroom” by Eric Meyer (= Eraticus) – Photo taken by Eraticus.CC BY-SA

Vitamin D helps absorb calcium which is stored in our bones and vital to our health. Calcium keeps our hearts beating and is involved in our blood clotting. If you don’t get enough vitamin D over a long period of time your bones will become weaker as the calcium is slowly used up.

Vitamin D also helps in other processes in the body including maintaining a healthy immune system and regulating other hormones like insulin. It also boosts our mood which is perhaps why when the sun comes out everyone is happier. Whilst vitamin D deficiency is common in winter, it isn’t the same thing as Seasonal Affective Disorder.

A small study showed that the slapdash way most people apply sunscreen means they still get enough vitamin D. Those at risk of not having enough are pregnant ladies and babies (who often get supplements), older people, people who live in institutions and people at higher latitudes who have darker skin and cover up a lot.

Vitamin D Deficiency

Vitamin D Deficiency

This diagram collates vitamin D status studies from around the world. Is vitamin D deficiency a major public health problem?

We shouldn’t cover up all the time, but tanning, and especially burning our skin, can cause lots of damage which we don’t notice until later in life.

For further information on the electromagnetic spectrum, check out our Beyond the Rainbow” show, filled with UV demonstrations and more.

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Posted in Biology, Exploring Science, Physics, Space
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