Reviewed by Sanny Chan, MD

Molds are a kind of fungus, the most common found on earth. There are 1.5 million species of mold, making up 25 percent of the earth’s biomass. However, only 80 species are known to trigger allergic reactions.

Many types of molds (microscopic fungi) live in our environment. Mold grows in indoor and outdoor areas that are warm, dark and/or moist. Molds reproduce and grow by sending tiny spores into the air. Inhaled spores cause allergy and asthma symptoms. Examples of allergy symptoms include itchy eyes, runny nose and rash.

Mold grows easily in most humid, warm conditions, but it also can occur in conditions that are cool and, rarely, even dry. A common name for mold found indoors is mildew. Mold spreads by way of spores, which are like tiny airborne seeds. Most mold in the home originates outdoors. Mold spores can waft in, or be carried in on clothes. Mold finds hospitable ground and colonizes in wet basements, humid crawl spaces, and anywhere leaks, high humidity or condensation are present.

The microscopic spores that mold uses to spread and reproduce are the primary culprits in mold allergies. When inhaled, they can cause respiratory allergic symptoms and, potentially, other health problems. Although mold growth isn’t a reason to panic, large areas of mold growth may require a special cleanup in order for a residence to be habitable.


Factors that Influence Amount of Mold 

The amount of mold growing inside your home depends on these factors:

  • How much moisture is or was in the area
  • How long the area stayed wet
  • How much air circulates in the area to dry the moisture
  • How many times the area has been wet
  • How much sunlight comes into the area

It may not be possible to eliminate all mold spores from your home environment, but reducing moisture can make the environment unsuitable for mold to thrive.


Reduce Mold Exposure 

Once an allergy has been identified, your healthcare provider may recommend medications or therapies to control symptoms. The next step is to decrease or eliminate exposure to the allergen. This is called environmental control. Evidence shows that allergy and asthma symptoms may improve over time if the recommended environmental control changes are made. Here are some environmental control measures to consider:

  • In the bathroom
    • Use an exhaust fan or open a window to remove moisture after showering.

    • Wipe down the damp surfaces after showering.

    • Wash bathrooms with a mold-preventing or mold-killing solution at least once a month.

  • In the kitchen
    • Use an exhaust fan to remove water vapor when cooking.

    • Discard spoiled foods immediately.

    • Empty the garbage daily.

    • Empty water pans below self-defrosting refrigerators frequently.

  • Around the home
    • Remove moldy stored items.

    • Vent the clothes dryer outside.

    • Remove leaves, clippings and compost from around your house.

    • The person with a mold allergy should avoid cutting grass and raking leaves or wear a facemask for these activities.

    • Keep the indoor moisture low. The ideal humidity level is 30-40 percent. In warm climates, use a dehumidifier or central air conditioning to control the temperature inside your house. Central air conditioning reduces indoor humidity. Clean the dehumidifier regularly.

    • Avoid using humidifiers. Humidifiers and vaporizers will increase humidity in the room and create a favorable environment for mold growth. Additionally, they can inadvertently spread mold spores throughout your house. If you must use a humidifier, prevent mold growth with proper humidifier care.


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