With the long, hot Australian summer comes the imperative to manage the country’s enormous skin cancer risk.

Along with the growing raw numbers (11,545 skin cancer cases diagnosed in 2009) and rates of melanoma, the numbers of non-melanoma skin cancers (NMSC) are going off the charts. Men are disproportionately affected, with one in 14 blokes diagnosed with melanoma before the age of 85, compared with one in 23 women.

Two months ago the Medical Journal of Australia reported the total number of NMSC treatments increased from 412,493 in 1997 to 767,347 in 2010, and the authors estimated the number of treatments would increase to 938,991 by 2015.

The costs estimate – which I understand doesn’t include the patient’s out-of-pocket expenses – was over half a billion dollars in 2010. This is an enormous health burden unique to Australia and our friends across the Tasman.

Slip, slop, slap was born to help Australians adapt to the unique environment in which we live. More recently we’ve added seek (shade) and slide (on sunglasses) to slipping (on the shirt) and slapping (on the hat). But it’s the slopping on of sunscreen that has caused the most controversy in the almost 20 summers during which I’ve been banging on about skin cancer.

Almost every summer I’ve been brought in to the newest debate about the dangers, the changes, the failings or the confusions about sunscreen. And this summer is no different.

This summer attention has focused on the introduction of the new standard of SPF50+. When it comes to SPF50+ the story is a reasonably simple one. A little better than SPF30+ is good – but we still need to put enough of the stuff on to achieve the claim on the bottle.

Sunscreen is usually applied in half or less of the dose necessary to achieve the sun protection claimed on the bottle.

What does the SPF number mean?

SPF stands for Sun Protection Factor and the number reflects how protective a sunscreen is against UVB radiation, which causes sunburn and increases skin cancer risk.

SPF15, for example, filters about 94% of UVB radiation, leaving about 1/15th of the radiation getting through. But it also means skin that would normally burn in 10 minutes in the midday summer sun would take about 150 minutes or 15 times as long before the burn would occur. So the lotion “screens” but does not “block” the sun.

For SPF30+ it’s the same story: about 1/30th gets through so 96.7% of the UVB rays are filtered out. And with SPF50+ – you guessed it – 1/50th gets through, or about 98% is filtered out.

So while there might sound like a world of difference between the numbers 30 and 50, we’re talking just 1.3% improvement in UVB protection.

The new standard applying to sunscreens claiming an SPF in excess of 30+ will require a better standard of UVA protection and this is probably the most important advance in this recent change. Also, misleading claims of sunscreen being “waterproof”, “sweat proof” or the term “sunblock” are no longer allowed.

Sun protection

It’s important to understand that sunscreen is a useful adjunct to other sun protection measures. Rather than being our first line of defence, it should be the last. Not only do we seldom use enough, but it’s easily sweated off and rubbed off as we towel down or rub water from our eyes.

But why should we bother to mess about with the funny white creams anyway? Can’t we just wear protective clothing, hats and use shade, or better still stay indoors?

Well, of course we can and should use all these strategies. But sunscreen is a sun protection strategy proven by randomised controlled trial to prevent skin cancer.

The Nambour study conducted in South East Queensland in the early 1990s found the use of sunscreen (then the old SPF15+) reduced the risk of squamous cell carcinomas (the second most common non-melanoma skin cancer) by 12% and melanoma by about half.

So, as we get closer to seeing SPF50+ sunscreen land on the shelves of our local shops remember the famous all-encompassing 1998 life advice speech of disputed origins “Wear sunscreen” – and heed the advice. It’s still a good tip.

Here are a few other simple sunscreen tips:

1. Sunscreen shouldn’t be used as the first and last defence against the sun. Don’t forget the other “S”s – Slip on a Shirt, Slap on a Hat, Seek some shade and Slide on your sunnies.

2. Don’t throw out the old SPF30+ sunscreen. Cancer Council Australia recommends using any water resistant, broad-spectrum sunscreen with an SPF of at least 30, so use up what you have.

3. Whether it’s current SPF30+ or the new SPF50+ sunscreen, put plenty on. About a teaspoon for each limb and a teaspoon for the front of the body and one for the back.

4. Reapply every two hours. Regardless of the SPF, all sunscreens can be washed off, towelled off or wiped away when we rub that last wave out of our eyes.

5. Learn to read the UV index. Under UV three you can get some safe sun time and a little vitamin D.