A breathing valve, also known as an exhale valve, is a one-way valve typically found in masks or respirators. Its purpose is to allow air to be exhaled easily while preventing unfiltered air from entering the mask.

The valve works by opening when the wearer exhales and closing when they inhale. This allows for easier and more comfortable breathing, particularly during extended use.

However,the use of breathing valves in masks has been debated during the COVID-19 pandemic. While they may provide more comfort for the wearer, they may not provide as much protection for others since they allow unfiltered air to be exhaled. As a result, some health experts recommend against the use of masks with breathing valves in certain settings, particularly in situations where there is a higher risk of spreading COVID-19.