Sunday, July 17, 2011

Sunscreens, SPF 50


Much excitement in Australia this week with the granting of permission to sell SPF 50 sunscreens.

Got to be 66% better than all those SPF 30 ones, mustn't they?

Well, hold you horses. Could it just be marketing hype?

To get the SPF factor, you divide 100 by 100 minus the percent of the UV radiation blocked.

So if a sunscreen blocks 90% of the UV light, its SPF is 100/(100-90) = SPF 10.

95% = SPF 20

97% = SPF 30+

98% = SPF 50.

So paying the extra money for an SPF 50 sunscreen will increase your protection by just 1%.

If (IF!) it is re-applied regularly and applied at the same thickness as is used in the test (0.1mm).

T-shirts and a hat have a higher SPF factor.


  1. Nah. Serious vitamin D deficiencies.

    Interestingly the burqa isn't seen in photos of Islamic cites of the early 20th century. So a power and control issue, not a religious one.

  2. What I want to know is why the bedouin prefer black to white as a means of sun protection in their clothing. Whenever I've worn black in hot climes, it's been unbearable, but my clothing is not as loose as a tribesman's outfit.

  3. To generalise, it's like the stats in the news that say.."Will double your risk of xyz", but they don't tell you that the xyz risk is 1 in 10,000, so doubling it makes it 1 in 5,000. Which means there's a 99.98% (rather than a 99.99%) chance you won't get it.

    Actually, it's not really like that at all, but that's what your post made me think of. :)


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