Like any piece of clothing or accessory, your mask cushion becomes worn out over time.
The life of a mask cushion depends on various factors such as the oils from your skin, and how often you clean it. We highly recommend inspecting your mask according to the cleaning and maintenance routine outlined in your mask user guide. The user guide supplied with your mask contains guidelines to help you inspect, assess and replace your supplies.
Check for small tears or pinholes and anything else that might cause a leak. Household pets (and children) have been known to damage cushions by playing with them, so it's a good idea to keep your mask out of reach. Also, be sure not to leave your mask somewhere that receives direct sunlight during the day.
Because the timing and reasons for replacing your mask cushion greatly depends on your mask, it's important to reference your mask user guide for specific details.