It is especially a good idea to have sunscreen on hand when you have children. It is just too difficult to keep them out of the sun so apply the sunscreen and let them be.
Remember that it needs to be reapplied every 3-4 hours. If you are planning to spend all day at the pool then you may need to apply it more than once.
Many places provide shade next to pools now. Reserving cabanas are great ways to minimize the amount of time your skin sees the sun. If you are smart about it you can literally spend all day at the pool and come out with beautifully protected skin.
If you should happen to notice your skin getting a little pink then that is your signal to take cover.
Sunburns are miserable and cause permanent damage to your skin. If you are not finished at the pool or outside it would be wise to spend the rest of the time under some shade.
If you are not finished at the pool or outside it would be wise to spend the rest of the time under some shade. Same goes for exercising outside in the hot summer sun. If you have bright white skin and you choose to go for a 4 mile run without sunscreen you will most likely get a sunburn.
I actually keep my treadmill and workout equipment in my garage for convenience purposes. I find I use it more often when it is already out.
If there are summer days where you need to work out at home or outside then by all means do but at least provide yourself the option of working out inside or under a shaded area.
This way your skin will be protected from the hot rays of the sun and your workout can go on without interruption.