What do creaking floors, condensation and sneezing have in common? Each can be related to the humidity level in your home. And it doesn't stop there. Damage to wood floors and electronic equipment, increased dust, respiratory problems, throat and skin irritation, rot, pests, mold and mildew, dust mites and allergies are other common problems that result from indoor humidity levels that are either too low or too high.

Humidity is the amount of water vapor in the air and is caused by many factors. Cooking, bathing and doing laundry all produce water vapor and, thus, raise indoor humidity. Running your home's heating system can keep you warm during the winter, but it can cause your house to become too dry when heaters and cooler temperatures combine to lower the moisture levels in the air.

Dry home syndrome is common in older, less energy-efficient homes—homes that are not as tight as new homes; drafts can lower indoor humidity. The reverse is true with a tight, more energy-efficient modern home. The lack of free exchange of air can cause high indoor humidity levels.

An indoor humidity level less than 30 percent is too dry. Such a level can cause dry nose and throat and colds; wall paneling, wood trim and hardwood flooring can shrink and cause joints to open; cracks in drywall and plaster can develop; joints in wood furniture can become loose, and pianos can go out of tune. If you find yourself being shocked by static electricity as you move about your home, your home's indoor humidity is too low. Skin irritation and respiratory problems are other telltale signs.

Conversely, a home that is too wet—where the humidity is greater than 50 percent—can be a breeding ground for mold, rot, pests such as termites and cockroaches and condensation. Excess humidity can produce enough condensation to result in staining on ceilings and walls and cause flaking paint and peeling wallpaper. In warmer climates, the combination of high humidity and heat provide the optimal environment for pests and mold. If you live in an area where termites are pervasive, you have a lethal combination that can, if you don't take preventive action, make your home one big science experiment. While it's true that dryness is more common in the cold north, many homes throughout the country experience the same problems when the weather turns cold. However, more often than not, homes contain enough sources of indoor moisture (cooking, clothes drying, showering) to balance the moisture losses in winter and keep humidity at a comfortable level.

An effective means of dealing with dry home syndrome is to use either a portable or whole-house humidifier. The most common type is an evaporative humidifier wherein a reservoir holds cold water and dispenses it into a basin. A wicking filter absorbs the water from the basin and a fan blows air through the moistened filter. As the air passes through the filter, it evaporates some of the water there. The higher the relative humidity, the harder it is to evaporate water from the filter, which is why a humidifier is self-regulating (as humidity increases, the humidifier's water-vapor output naturally decreases).

Sometimes an evaporative humidifier will be hooked up to the heating and cooling system of a house or building. These systems work in a similar way. A metal mesh or screen is located in the duct coming from the furnace and-or air conditioner. Water from the building's pipes flows down the screen. As air coming from the duct blows across the screen, it picks up moisture.

If your home is too wet, you can lower the humidity by installing exhaust fans in the bathrooms, kitchen, laundry and any other space where water vapor is created. You may also need a dehumidifier, which in contrast to a humidifier removes moisture from the air. The usual technique to remove the moisture is to condense it onto a cold surface. Anyone who has poured a cold glass of iced tea on a hot, humid summer day knows that moisture will condense on the glass. When air cools, it loses its ability to hold moisture. In the case of the cold glass, the moisture in the air condenses right onto the glass. If the glass is left on a table long enough and if the air is very humid, a significant puddle of water will form. You may have noticed the same phenomenon in an air conditioner. The moisture in the air inside the room condenses onto the air conditioner's cold coils. If it's a window unit, the water drips out the back of the unit onto the ground.

Excessive indoor humidity is removed with a dehumidifier which is essentially an air conditioner that has both hot and cold coils in the same container. A fan draws humid air over the cold coil of the air conditioner to condense moisture, which then drips into a collection container. Dry air passes over the hot coil to restore it to its original temperature. Air conditioned space should not need a dehumidifier since it acts as one.

For best indoor comfort and health, a relative humidity of about 45 percent is ideal. You can track your home's humidity with an inexpensive hygrometer. You might be surprised to learn how low it is.