spf 30 is effective because it provides protection from both uva and uvb rays. when spf is greater than 30 it should mean that in addition to chemical sunscreens the makers have included titanium dioxide and/or zinc oxide which provide physical barriers and are actual sunscreens. irrespective of the spf you’ll need to reapply the sunscreen every 2 hours.
does sunscreen with an spf over 30 actually work or are the claims for anything over 30 just hype?