A cleaning in order so that the air circulates again in the bathroom.
Turn off the power supply.
Unscrew the fastening screws to extract the block from the aerator by releasing a part of the exhaust duct.
Remove the engine block from its housing to gain more convenient access to both sides of the fan blades.
Scrape off the bulk of the dust with the tip of a knife.
Finish with an old toothbrush and some water with dishwashing liquid.
Reassemble the engine block: Using a pair of pliers, pull the rubber "silent block" through the crankcase mounting holes.
Then replace the aerator.
Vacuum the bathroom aerator regularly, as moisture sticks dust on the blades and eventually blocks the engine.