A few things to remember when you use sunscreen are:
Put it on at least 30 minutes before you go out. Sunscreen will not work well until it is absorbed into the skin. This is the number one mistake people make. They will wait until they are laying on the beach to put on the sunscreen.
- Use the highest SPF rating you can find. SPF 50 is good for fair skinned people.
- Reapply often. Perspiration, swimming and time remove sunscreen.
Use a waterproof sunscreen if you will be near water and reapply after swimming.
The SPF rating is based on how much "added" protection it will give the "average" person. A SPF 15 means that if you burn in 10 minutes you will achieve the same burn in 150 minutes. It doesn't mean it will stop you from burning. A SPF of 50 means you will burn in 500 minutes. (Around eight hours) However, it will have worn off long before eight hours and should have been reapplied.