High Quality Content by WIKIPEDIA articles! A dehumidifier is typically a household appliance that reduces the level of humidity in the air, usually for health reasons. Humid air can cause mold and mildew to grow inside homes, which pose various health risks. Very humid climates or air make some people extremely uncomfortable, causing excessive sweating that can`t evaporate in the already-moisture-saturated air. It can also cause condensation that can disrupt sleeping, or prevent laundry from drying thoroughly enough to prevent mustiness. Higher humidity is also preferred by most pests, including clothes moths, fleas, cockroaches, Woodlice and dust mites. Relative humidity in dwellings is preferably 30 to 50 percent.