Bathroom extractor fans

The issue is most likely condensation. Probably be better with a dMVHR — decentralised Mechanical Ventilation with Heat Recovery. A dMVHR unit works through an external wall and recovers heat from the warm stale air being extracted, transferring much of that heat to the fresh incoming air. So it doesn't generate heat like a heater, but the incoming air is warmed by recovered heat. As opposed to a standard fan, which to be honest is a tick box exercise rather than being truly effective in bathrooms

While the ideal solution is as suggested by Bathroom Adaptions Limited, In a majority of homes this is not physically or financially viable. The main cause for damp is due to lack of ventilation and heat source, you can check if the heat source in the bathroom has a large enough BTU output, usually in bathrooms the towel rail warmer is used to store towels on constantly , this restricts the amount of heat that is emitted. So check your Towel rail warmer / radiator size and make sure it is correct for the room, also only put towels on the radiator to warm them , not all the time. I hope this helps. Stef Handyman