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When you’re in a car, train or bus, do you choose a seat to avoid being in the sun or do you like the sunny side?

You can definitely feel the sun’s heat through a window. But can you get sunburn or skin damage when in your car or inside with the windows closed?

Let’s look at how much UV (ultraviolet) radiation passes through different types of glass, how tinting can help block UV, and whether we need sunscreen when driving or indoors.

What’s the difference between UVA and UVB?

Of the radiation that reaches Earth, about 95% is UVA and 5% is UVB.

UVB only reaches the of our skin but of sunburn, cataracts and skin cancer.

UVA into our skin and causes cell damage that leads to skin cancer.

Glass blocks UVA and UVB radiation differently

All used in house, office and car windows completely blocks UVB from passing through.

But only laminated glass can completely block UVA. UVA other glass used in car, house and office windows and , increasing the risk of cancer.

Car windscreens block UVA, but the side and rear windows don’t

A car’s front windscreen lets in lots of sunshine and light. Luckily it because it is made of two layers of laminated glass.

But the side and rear car windows are made of tempered glass, which doesn’t completely block UVA. A found a range from 4% to almost 56% of UVA passed through the side and rear windows.

The UVA protection was not related to the car’s age or cost, but to of glass, its colour and whether it has been tinted or coated in a protective film. Grey or bronze coloured glass, and window tinting, all increase UVA protection. blocks around 95% of UVA radiation.

In a separate study from Saudi Arabia, researchers fitted drivers with a . They found drivers were exposed to UV index ratings up to 3.5. (In Australia, sun protection when the UV index is 3 or above – at this level it takes pale skin about 20 minutes to burn.)

So if you have your windows tinted, you should not have to wear sunscreen in the car. But without tinted windows, you can accumulate skin damage.

UV exposure while driving increases skin cancer risk

Many people spend a lot of time in the car – for work, commuting, holiday travel and general transport. Repeated UVA radiation exposure through car side windows might go unnoticed, but it can affect our skin.

Indeed, skin cancer is more common on the driver’s side of the body. A (where drivers sit on the left side) found more skin cancers on the left than the right side for the face, scalp, arm and leg, including 20 times more for the arm.

found this effect was higher in men. For , an early form of melanoma, 74% of these cancers were on the on the left versus 26% on the right.

Earlier Australian studies reported more and more on the right side.

Cataracts and other eye damage are also of the body.

What about UV exposure through home or office windows?

We see UV damage from sunlight through our home windows in faded materials, furniture or plastics.

Most glass used in residential windows lets a lot of UVA pass through, .

Single-pane glass lets through the most UVA, while thicker, tinted or coated glass blocks more UVA.

The best options are laminated glass, or double-glazed, tinted windows that allow less than 1% of UVA through.

are made from laminated glass, which completely stops UVA from passing through.

Most office and commercial window glass has better UVA protection than residential windows, allowing . These windows are usually double-glazed and tinted, with reflective properties or UV-absorbent chemicals.

Some that reduce heat using chemical treatments to darken the glass can also block UVA.

So when should you wear sunscreen and sunglasses?

The biggest risk with skin damage while driving is having the windows down or your arm out the window in direct sun. Even untinted windows will reduce UVA exposure to some extent, so it’s better to have the .

For home windows, can increase UVA protection of single pane glass. UVA blocking by glass is similar to protection by sunscreen.

When you need to use sunscreen your skin type, latitude and time of the year. In a car without tinted windows, you could burn after one hour in the middle of the day in summer, and two hours in the middle of a winter’s day.

But in the middle of the day next to a home window that allows more UVA to pass through, it take only 30 minutes to burn in summer and one hour in winter.

When the UV index is above three, it is recommended you while driving or next to a sunny window to avoid eye damage.

, Associate Professor of Medical Sciences,

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