Any humidity of 30 percent or less is considered low and can be dangerous. Low humidity can cause breathing difficulties, discomfort and may damage a home's foundation.
While the humidity of outdoor air cannot be controlled, the humidity of a home's air can be controlled with humidifiers and dehumidifiers. Just as the humidity can be too low, it can also be too high. The point at which there is too much moisture in the air is about 50 percent humidity. Beyond this level of moisture, things like mold and bacteria can grow quickly and cause both short-term and long-term breathing problems.