Good ventilation is important for the whole house but vital in kitchens and bathrooms which create a lot of moisture. High humidity rooms that aren't properly ventilated can cause ongoing problems with condensation, damp, and black mould. Persistent moisture from cooking, bathing and laundry tasks may even spread, causing damp in other areas of the house.
Mechanical extractor fans are an excellent, cost effective way to remove moisture from the air. Luckily, there are several simple one box solutions that typically contain all the elements an average household needs.