Features

Skimping on sunscreen sells your skin short

by Cathy Johnson

How long does a 110 ml tube of sunscreen last you? If you've used it more than three times to cover your whole body say, at the beach, then you haven't been using enough for proper protection.



[Image source: iStockPhoto | CentralITAlliance ]

If you think sunscreen doesn't work as well as it should, it might be that you're not using enough.

Sunscreen is sold in containers of all different shapes and sizes, but the 110 ml tube is a popular choice.

If you're aiming for whole body coverage (say, at the beach) though, and you use a 110ml tube more than three times, you haven't been using enough.

"It's very well known that people don't put enough sunscreen on," says John Staton. He's Australia's only tester of sunscreen SPFs, which refers to the length of time it takes for your skin to burn when you are in the sun while wearing sunscreen, and a representative of Standards Australia on a number of overseas sunscreen standards committees.

In fact, research shows people typically use only 25 to 75 per cent of the amount used by testers in the process that determines the SPF number on the container.

Since the protection factor varies with the amount of sunscreen applied, that means most users probably achieve a level of protection 20 to 50 per cent of that expected from the SPF on the label.

So your SPF50 might really giving be you as little as SPF10.

Teaspoon at the beach?

Advice given by health experts about how much sunscreen to use is often given in 'teaspoons'.

You should apply about one teaspoon per limb, one each for the front and back of the torso, and one for the face and neck. That's a total of seven teaspoons.

But very few of us take a teaspoon to the beach.

Seven teaspoons is 35 mls, "virtually a cupped handful", Staton says.

"You know you've only got to look at when people buy a 100 ml bottle and they use it ten times, you know you've underutilised it by about two thirds."

Like painting a brick wall

To understand why the amount of sunscreen matters, you need to recognise the surface of skin is not smooth but has lots of tiny dips and grooves on it, Staton says.

You need to apply enough sunscreen to fill those dips, he says.

"Until you fill the skin so you've got a continuous film, you're not anywhere near fully protected. Once you've done that, the amount you put on top of that is going to give you the extra protection."

Terry Slevin, education and research director at Cancer Council WA, likens applying sunscreen well to trying to paint a brick wall, where the mortar between the bricks sits at a lower level.

Two coats of paint are almost always needed for satisfactory coverage. With the first coat, the dips between the bricks where the mortar is can still be seen. It's often only with a further application that the mortar lines are covered and the surface becomes more featureless.

In an ideal world, this would mean applying a second sunscreen coat 15 to 20 minutes after the first coat has been applied, allowing "time for the first coat to bind to the skin and dry a little and penetrate slightly deeper into the skin", Slevin says.

Further reapplication of sunscreen is needed after vigorous activity that could remove sunscreen, such as swimming, towelling, excessive sweating and rubbing.