How often should you wash your backpack?

As a cryptocurrency and finance professional, I'm not typically tasked with answering questions about backpack hygiene. However, if I were to approach this question from a practical perspective, I would inquire: "How frequently should one clean their backpack to ensure it remains in good condition and hygienic? Is it necessary to wash it after every use, or can it be cleaned less often depending on the materials it's made of and the activities it's used for? Additionally, what cleaning methods are recommended to avoid damaging the backpack or its contents?