A dehumidifier is typically a household appliance that reduces the level of humidity in the air, usually for health reasons. Humid air can cause mould and mildew to grow inside homes, which has various health risks. 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. Relative humidity in dwellings is preferably 30 to 50%. Dehumidifiers are also used in industrial climatic chambers for keeping desired humidity levels.