Using the wrong bleach
If you choose to bleach your cloth masks when washing them, make sure you know which bleach to use. The CDC recommends ensuring your bleach is meant for disinfecting and using bleach with between and 5.25 and 8.25 percent sodium hypochlorite. Do not use a bleach that doesn’t specify the levels of hypochlorite. Be sure to rinse your mask thoroughly after using bleach on it, and giving it plenty of time to ventilate after washing and before using it.