Mask fit testing is a process that determines if a particular type of respirator or face mask fits an individual's face properly and provides adequate protection against airborne hazards. It involves the use of a test agent, such as saccharin or Bitrex, to determine if the mask wearer can detect the agent's taste or smell while wearing the mask. If the test is successful, it indicates that the mask forms a tight seal around the wearer's nose and mouth and is providing adequate protection against airborne hazards. Mask fit testing is important for individuals who work in environments where respiratory protection is necessary, such as healthcare workers, construction workers, and industrial workers.