Inside a hearing instrument are tiny wires, switches, electronic circuits, a microphone and a speaker. These components are tightly packed inside the instrument and surrounded by a plastic shell. Moisture, corrosion and shock are the enemies of hearing instruments. In normal use a hearing instrument comes in contact with perspiration which is not only watery but also corrosive. These filters change the frequency response of sound produced by the hearing instrument.
Excessive humidity can totally block the sound coming through the earhook.
Then unscrew the earhook carefully and use an airbulb to dry out the filter. Ask your hearing instrument dispenser for more information on how to control humidity and moisture. There are devices like Oticon's WaxBuster, standard on all Oticon ITEs, that are effective in preventing ear wax damage. Shock from dropping an instrument can dislodge the wiring or induce physical contact between components. Both can affect instrument performance.