Why do I need to reapply SPF?
No matter what SPF rating you're wearing, it doesn't last all day. There are many different things that will cause the sunscreen to break down. For example, if you touch your face a lot, then you're rubbing off sunscreen. If you're sweating a little bit (we all perspire without even noticing it), those oils in our skin interact with the sunscreen and start breaking it down. If you apply sunscreen in the morning, even if you are not outside, you need to reapply by midday.