Always apply enough and in advance - if you can, 20 minutes
before sun exposure, as it needs to be absorbed by the skin to
offer the maximum protection and never forget that even on cloudy
days you are exposed to damaging ultra-violet radiation. When it
comes to the SPF value always go higher as you need to take many
factors into account - the intensity of UV radiation levels vary at
different times of day, your genetic make-up, if you are in and out
of water etc.