What is a dehumidifier? Dehumidifier is a household appliance that reduces the level of humidity in the air, commonly it is for health reason. The humidity in the house is highly affected by the changes in the weather. There is a greater possibility of high level of humidity when it is cold and raining. I remember one time that one of our cabinets grows a few molds on it. It’s really unpleasant to look at. Perhaps one dehumidifier UK in the house can make the humidity level normal and it can also stop the threats of fleas and cockroaches.