» About     » Archive     » Cast     » Authors     » Submit     » Search     » Random     » Statistics     » Forum     » FAQ     » Video Game     » RSS Feed     Updates daily

No. 185:

First | Previous | 2009-06-10 | Next | Latest

First | Previous | 2009-06-10 | Next | Latest

Generated by an infinite conga-space of monkeys coerced by: Ben Carr

The author writes:

Ever wondered what the SPF number of a sunscreen means?

SPF X means that if it takes you T minutes to burn normally, then you will burn equally in XT minutes after proper application (about 30 grams across your body) of that sunscreen.

SPF 10 means that you should burn 10 times more slowly, by blocking out 90% of the sun's ultraviolet rays. SPF 100 means that you should burn 100 times more slowly, by blocking out 99% of the sun's rays.

In general: SPF X means that you should burn X times more slowly, by blocking out (100 - 100/X)% of the sun's rays.

You can infer from this that applying half the recommended amount blocks out only a quarter as much sun (taking the square root of the SPF rather than halving it). And in fact most people do under-apply sunscreen, using roughly half of the recommended amount. A half application of SPF 50 is the same as a full application of sunscreen with SPF of just 7 and a bit!