Most people spend as much as 90 percent of their lives indoors, so the quality of your indoor air is important. You'll feel better – and be healthier – if you can keep the humidity in your house as close to the 50 to 55 percent level as possible. You can measure indoor humidity using a hygrometer, also known as a humidity or moisture meter.

If the humidity is too low, your house may crackle from static electricity and your sinuses, throat and skin feel dry. Dry air can cause sinus membranes to dry out, crack and become vulnerable to inflammation and infection. Dryness can also cause wall paneling, wood trim and hardwood flooring to shrink and joints to open.

The air is generally drier in the winter because cold air holds less humidity than warm air. Winter dryness in houses is frequently due to having too much dry outdoor air exchanged for the more humid indoor air. In cold weather, outdoor air is pulled into the home because of the "stack effect" – warm air rises and leaves through gaps in the upper part of the house and is replaced by cold dry air that enters through cracks in the lower portion. Houses with gas heating can be more susceptible to this effect because leaky ducts and chimneys contribute to accidental ventilation whenever the furnace is running. If the heating and cooling system ducts leak, that can also create negative pressure that pulls outdoor air into your home.

While many homeowners seek to solve the problem of overly dry air by adding a humidifier, the best approach is to improve the home's heating and cooling system and add caulking and insulation.

Leaky, poorly insulated houses can also contribute to excess humidity. In summer, the more humid outdoor air enters the home, and in winter, water condenses on the cold surfaces of uninsulated glass.

Signs of high humidity include condensation on cold surfaces and mold and mildew growth. Excess humidity in your home can lead to mold growth and increase the dust mite population, and both mold and dust mites are powerful allergens. Reducing indoor humidity below 60 percent will reduce mold and cause dust mites (microscopic spiderlike insects that cause many people allergy problems) to go dormant.

Here are some ways to keep the moisture in your home at a comfortable level

• If you are installing a new heat pump, air conditioner or furnace, make sure the contractor sizes it properly for the size of your home. If the unit is too large, the unit won’t cool long enough to remove interior humidity in the summer.
• Eliminate air leaks in the ductwork for heating and cooling systems.
• Use bathroom and kitchen exhaust fans to remove moisture to the outside. Vent your clothes dryer to the outside.
• Make sure the ground slopes away from the foundation, so that water flows away from the house.
• Clean out gutters regularly
• Fix plumbing and roof leaks.
• Put a plastic cover over dirt in crawlspaces to prevent moisture from coming up from the ground.
• Caulk and weather-strip windows and doors.