How long do tans last in Island Living?

This has been a question I have had ever since I gave my sim their first tan in Island Living. They got a perfect tan. Afterward, I figured it would wear off after the moodlet went away, but no. A sim day went by and it was still there. Then two. I sort of gave up and just kept playing. I didn't pay attention to how many days went by, but eventually, it did go away. I just would like to know if anyone has figured out how many sim days the tan lasts.