The Everyday Home: Humidity leads to mold growth

Sonya McDaniel, extension educator, FCS/CED
Pottawatomie County Extension Service

With all of the recent rain and flooding, when the sun comes out and humidity rises, a perfect environment is created for mold growth. 

“Many home owners may begin to see mold and mildew growth increase in or around their homes this summer.” says Sonya McDaniel, Pottawatomie County Family and Consumer Science Extension educator. “Mold requires moisture, warm temperatures and nutrients to reproduce, and in our area we have plenty of each this year.”

Mold is a form of fungi and a part of nature. Just as other plants produce seeds to reproduce themselves, mold produces tiny spores to reproduce itself. These spores are floating through outdoor and indoor air and water at almost all times.  Warm and humid weather provides excellent conditions for mold to grow.

Mold can have harmful effects on human health. We can be exposed to mold either by touching it or by breathing air that contains mold spores. This exposure may cause allergic symptoms and health problems. Reactions differ from person to person, but can include sneezing, coughing, runny nose, sinus problems, nosebleeds, asthma, skin and/or eye irritation, headaches, difficulty concentrating, and even memory loss.

Mold is also destructive to buildings and property. When mold spores grow, they decompose and digest the surface that they are growing on. This results in damage to buildings and discoloration and deterioration of furniture, books, and other items.

Mold spores are so small that they are invisible to the naked eye. They exist almost everywhere, in indoor and outdoor air. It is not really possible to eliminate mold spores. Instead, we can prevent indoor mold growth by controlling moisture in the air, eliminating nutrient sources, and controlling temperatures.

Control moisture in the air. Moisture control is the key to mold control. Mold spores cannot grow without water. Moisture in our houses comes from many sources. Outdoor moisture can come into our houses either as damp air or as water. It enters through doors, windows, and other openings, such as cracks. We also make moisture inside our house by breathing, cooking, dishwashing, showering, and doing laundry. To prevent mold, dry out any excess moisture and try to prevent moisture from entering the home.

Keep your house clean and eliminate nutrients. Many materials in homes provide a ready source of nutrients for mold. Mold can feed on natural fibers used in clothing and furnishings, paper products, glues, such as those sometimes used in book bindings, and materials in some grout. Some materials, such as ceramic tile, glossy paint, and glass, do not support mold growth when they are clean. However, the slightest amount of soil on their surfaces will supply the necessary nutrients for mold growth. Soap "scum" left on shower stalls and shower curtains can provide the required nutrients for mold growth. Smoke and cooking oils also can settle on walls and furnishings and provide a soil on which mold will grow. Walls, closets, basements, clothing, and other textiles where mold is likely to grow should be kept clean in order to discourage mold.

Control the temperature in your home. Mold thrives at temperatures between 77°F and 86°F. Hot summer weather encourages mold growth. Air conditioning will reduce the interior temperature of homes, but if the air is humid, the temperature may not be uniformly low enough to stop mold growth. Pay special attention to the areas inside cabinets and closets and behind draperies and furniture. These places are often warmer than the rest of the house. Humidity will be trapped in these areas unless there is a way for air to circulate in and out.

Everyday Mold Prevention Tips

As we have shown, the best way to prevent mold growth in your house is to keep your house clean and dry. Here are some more tips from experts to prevent mold growth:

• Clean your house regularly.

• Remove food stains from furniture as quickly as possible.

• Clean showers and tubs weekly (or more often) so that mildew cannot grow on soap scum and moisture.

• Use fans to circulate the air.

• Keep closet doors open so air will circulate.

• Check the temperature and humidity in your house regularly. Try to keep indoor humidity below 60% relative humidity (ideally, it should be at 30-50%). Use a moisture or humidity meter to measure the relative humidity level. You can buy a small and inexpensive one at your local hardware store.

• Watch for condensation and wet spots. Fix moisture problems as soon as possible.

• Fix leaky plumbing.

• Perform regular heating, ventilation, and air conditioning (HVAC) inspections and maintenance. Keep HVAC drip pans clean, flowing properly, and unobstructed.

• Clean and dry wet or damp spots within 48 hours.

• Don't let foundations stay wet. Provide drainage, and slope the ground away from the foundation.

Source: University of Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences (UF/IFAS). Publication FCS3255.