Controlling Indoor Humidity

Step outside on a summer day, and it's easy to feel the effects of humidity -- sticky skin, a sweaty brow, air thick with moisture. But when it comes to humidity inside, those tell-tale signs are replaced by itching, sneezing and coughing, and they're not limited to the summer months.

Humidity makes you sneeze

The word humidity refers to the amount of water vapor in the air. So, how is it that microscopic water molecules can make you itch, sneeze and cough?

Those symptoms arise when people have allergic reactions to the organisms that thrive in humidity.

"Humidity promotes mold growth and dust mite population growth. Both are significant indoor allergens and can set off allergic sensitivity and can trigger rhinitis and asthma," said Dr. Michael Ruff, an allergist who works to raise awareness about asthma and allergies for the American Academy of Allergy Asthma and Immunology.

These are things that people can't see or feel, but they live on countertops, table surfaces, carpet, pillows, mattresses -- just about anywhere that people are, say experts. And they depend on warm temperatures and high humidity to live and grow.

If the presence of mold or dust mites sends you for a tissue or your doctor's office, then keeping the humidity inside your home at 50 percent or lower may provide some relief, said Ruff. Lower humidity will result in lower mold and dust mite growth.

Don't dry out

But, experts say, don't let the air inside your house get too dry. Skin irritation, difficulty breathing and static electricity are among common problems that develop when indoor humidity is too low.

Low indoor humidity is a bigger issue in winter months, when heaters and cooler temperatures combine to lower the moisture levels in the air.

A wet house

The airborne water can be detrimental to your home, as well as your health.

"High humidity in a home can cause rot. And, especially in the South, it draws pests. Bugs are always looking for water. Condensation provides [bugs] with the water they need," explained Jill Mayfield, Information Coordinator for Austin Energy Green Building Program, which helps Austin residents build more efficient homes and buildings.

"If you don't build properly, [moisture] can condense inside walls and cause rot. It's not obvious on the outside, but it could be rotting on the inside," she added.


If you suspect that the air in your home is too moist or too dry, then the first thing to do is verify the facts.'s Indoor Humidity Meter (at the bottom of this page) will help you determine what's happening with the water vapor inside your home.

Then, if the indoor humidity is too high, experts recommend you tackle the problem with dehumidifiers, ventilation, air conditioning and even what you put on your floors.

"Vent the areas that create moisture, like the shower or bathroom. Make sure you turn on the vent fans if you have them or consider having an electrician install one to the outside [of your home]. The same is true for cooking," explained Mayfield.

She added that contractors are willing to install humidifiers and other equipment that works in concert with your air conditioner to better control indoor air quality.

"If you're getting ready to install an air conditioner, make sure you size the unit properly. You need one ton of air conditioning for every 600 square feet of indoor space. If you size it correctly, then when the air conditioner runs, it may run a little longer, but it's pulling out the moisture. And it has an easier time cooling, so it's not costing you any more," said Mayfield.

She added that carpet can actually trap moisture, lowering indoor air quality. It's a double whammy for the soft floor covering, since Dr. Ruff points out that carpet is one of the favorite homes of humidity-loving dust mites.

If your home sits at the other extreme, and is too dry, then a humidifier could do the trick.

"It's simpler to put humidity in the house. Work with an air conditioning contractor to see how you can put a little more humidity in the home," advised Mayfield.