A dehumidifier is mostly a household appliance that reduces the level of humidity in the air, usually for health reasons, as humid air can cause mold and mildew to grow inside homes, which has various health risks. Relative humidity is preferably 30 to 50%.
Very high humidity levels are also unpleasant for human beings, can cause condensation and can make it hard to dry laundry or sleep. Higher humidity is also preferred by most insects, including clothes moths, fleas and cockroaches. Dehumidifiers are used in industrial climatic chambers for keeping certain level of humidity.