Western Australians have one of the highest rates of skin cancers in the world. Part of the message of Slip, Slop, Slap, Slide from the Cancer Council and Dermatologists for reducing the rates is the " slapping" on of sunscreen.

The sun protection factor (SPF) of a sunscreen refers to the length of time it takes your skin to burn in the sun when wearing a sunscreen. If you usually burn after 10 minutes without sunscreen, a SPF of 50 allows 500 minutes before burning. Sunscreens are tested for SPF using volunteers.  The Australian Standard for sunscreen testing requires the sunscreen to be applied at a rate of 2mg per square centimetre of skin. The sunscreen is spread over an area on a volunteer's back and allowed to dry for fifteen minutes. Another area is measured out without applying sunscreen on the same person's back. A lamp simulating ultraviolet radiation is shone on the area for different amounts of time, the following day assessors determine the smallest dose of UV light required to cause redness on both areas. For a SPF of 50+, the sunscreen has to achieve a minimum SPF of 60, the dose of UV light before burning is at least 60 times greater for the sunscreen protected area than the unprotected skin. Ten people are tested for every product and the results averaged. Water resistance is also tested with volunteers and a similar procedure, with the sunscreen being applied, allowed to dry and the person sitting in a spa and getting in and out at regular intervals for the duration of time claimed by the sunscreen before the UV light being applied as per the regular testing.

The SPF is only achieved with meticulous in the application, SPF 50+ cuts out 98%of the UVB, compare to 96.7 % cut out by SPF 30+ (not a doubling in protection)

Recently Choice checked six SPF 50+ and found that only two of the products met the label claim of 50+, the remaining products did offer high SPF though with a rating of SPF of 30 or more. Other consumer organisations in the UK (Which?), Consumer Reports in the US and Consumer New Zealand have found the same differences from those achieved by manufacturers despite the fact that labs are testing the same standard.

The human element may account for the variation in test results as different individuals burn at different rates, the sample size used is small and sunscreen deteriorates under certain storage and transport conditions (especially heat)

Aerosol sunscreens have the problem that the product is tested by weight before it is placed in the can with the propellant and the rating applied as per a lotion or cream.

For the best results from sunscreen apply

  • About two tablespoons for a whole adults full body coverage, using at least one teaspoonful for each limb, a teaspoon for both front and back and half a teaspoon for face, neck and ears.
  • 15-30 minutes before going into the sun, some of the protection can be more easily rubbed off before it has a chance to penetrate the top skin layers
  • Repeat every 2 hours, it is difficult to achieve a good coverage and sunscreen is a screen not a block
  • Check the expiry date, ideally replacing yearly
  • Store below 30C
  • Broad spectrum means protection against both UVB and UVA  as both types contribute to skin cancer and aging effects

To see the recommended sunscreens, go to and read the article for 'sunscreens put to the test'

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