I just wanted to point out, for those confused, that TashaFaun did NOT bump a 4 month old thread, but rather a "Thanks, this is great!!!11" post did.
Since it is bumped, I guess I'll comment on this, too, if it's of any use to anyone.
With suntans, I always click "Fix Tans & Burns" after I get my Sims back from vacation, and they NEVER keep their tan. I presume it's because I send them on such long vacations that by the time they get back they don't really have a tan anymore, but I haven't played the BV aspect in so long that I'm not entirely sure.