An earplug has an open inserting end, an open inlet end, a cover, a hollow body, a soft sheath, a tube and a sound-processing unit. The sound passes through the open inlet end, is processed by the sound-processing unit and then passes into an ear canal. Alternatively, RF (Radio Frequency) signals pass through the open inlet end and are processed by the sound-processing unit, and then radio signals pass into the ear canal. The soft sheath has a through hole. The tube is mounted through the through hole in the soft sheath and allows the open inserting end to communicate with the ambient air. Furthermore, the soft sheath and the tube are replaceable to conform to sanitary standards.