A room humidifier should be used in conjunction with moisturizing lotions for maintaining skin hydration--especially when the Dry Skin Index is elevated (6+). Otherwise, whenever the indoor relative humidity is below 40%, it's time to consider operating a room humidifier. The effectiveness of a humidifier depends on how much water vapor it emits and the size of the room. If the humidifier is undersized, it will not significantly improve indoor humidity or skin hydration. On the other hand, the release of too much water vapor may lead to conditions favoring mold formation. Since the optimum relative humidity for skin is about 60%, a humidifier should not increase indoor humidity above that level--check the DSI Sense app to make sure.