The answer to this question will depend on the type of reusable mask you’re using.
For example, experts don’t recommend washing the N95 respirators because it strips off the static filter that traps airborne particles. Instead, keep them in a breathable bag for one to two days before using them again.
But if you’re using a cloth face mask, it’s best to wash them at least once a day or as soon as they become soiled. Doing so keeps it clean, minimizes any risk of contamination, and maximizes its effectiveness.
John Hopkins Medicine recommends washing the cloth mask by hand or machine with hot water. If you’re handwashing the mask, it’s best to scrub it for at least 20 seconds before letting it dry.