Since very little is used in each application, it lasts a very long time. It’s hard to say how long as it depends upon how much and how often it is used. It typically lasts many years and you may never need to buy another unless you’ve loaned it out, lost it, want a new clean one, or are buying a gift for a friend.
The contents do not expire–they just eventually run out. Like powdered blush, you use so little that it seems to last forever until one day you notice it’s running out. If used enough eventually the pouch will be empty. Then you can buy a new clean one!
