http://community.thenest.com/cs/ks/blogs/beauty/archive/2007/11/08/how-many-times-should-i-reapply-sun-block-what-spf-do-i-have-to-use.aspxNormally, sun block reapplication depends on your activity level. If you plan on spending lots of time outside being active you should be reapplying every two hours. On a sunny summer day, Dr. Levine recommends SPF 45. Beyond the SPF(which only measuresenCommunityServer 2.1 SP1 (Build: 61120.2)http://community.thenest.com/cs/ks/blogs/beauty/archive/2007/11/08/how-many-times-should-i-reapply-sun-block-what-spf-do-i-have-to-use.aspx#186222Wed, 19 Mar 2008 00:08:56 GMTb16960c2-08ff-48dc-93ce-1f3c6b289aa0:186222CollegeGrrl219<p>It depends on how fair your skin is. If you can tan easily, than SPF 15 should suffice. However, if you are super pale like I am, SPF 50 is a must. I have actually gotten burned before using SPF 30. I actually wear SPF 30 moisturizer in the winter.</p> <p>Also, you should reapply every time it gets wet. If you are cool and dry all day, than once is enough. If you are swimming or sweating, you should reapply every 80 minutes or every time you towel off, whichever is sooner.</p>