Just like any other instruments, harmonicas also wear out. But it is not the whole harmonica that wears out but the reed. In almost all instruments, it is the vibration of the reeds that produce the sound. Even in a saxophone, the reed inside the mouthpiece is what produces the sound. The rest of the instrument just gives further tonal characteristics to the sound. But harmonica reeds are more durable than saxophone reeds. If you are somebody who plays the harmonica regularly, you can expect the reeds to last for around six months.