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.