Originally Posted by nibiyabi
I've found that anything above SPF30 or 35 seems to only have one difference between itself and its "weaker" brethren: price.
As for wanting to shield yourself from the sun but still attain a tan, I may recommend relaxing in the sun for 15-30 minutes (depending on temperature) before applying your sunscreen.
Coming from the country that has the highest skin cancer rate on the globe, I DO NOT recommend this. Tanning is dependent on the UV ray strength. This is not necessarily related to temperature, in fact not at all. If you use a sunscreen with an SPF rating of 15, you will get a tan. Note that you can still burn if you stay in direct sun too long. 30+ is better. Reapplication will most likely be necessary after swimming, dependent on the sunscreen you are using. Sunscreen should be reapplied regularly, at least hourly. Quite frankly if you don't regularly spend time in the sun, half an hour a day is the recommended maximum without sunscreen.
There are other factors that need to be considered such as skin type. I have an olive skin type which is less prone to burning and such. But I still burn if I do not take care.
Edit:- By the way this is not a dumb question, rather very sensible.