It’s important to wash your sleeping bag periodically to remove dirt, sweat and body oils. However, you don’t need to wash your sleeping bag after every camping trip. Instead, you can spot-clean dirt with a toothbrush and soap paste and air out your bag in the sun for a few minutes each day of your trip.
As a general rule, you should wash your sleeping bag once or twice a year, depending on how often you use it. If you use a sleeping bag liner, you may be able to go longer between washings.
When it’s time to wash your sleeping bag, make sure to follow the manufacturer’s instructions for washing and drying your sleeping bag. Improper washing and drying can damage the insulation and reduce the performance of your sleeping bag.
I hope this helps you know when to wash your sleeping bag!