It can lurk in your basement … it can hide in your shower curtains … it could be inside your pillow … or under your bed! The monster is mold, and it's a growing problem—and not just for people with mold allergies.

A fungi is not a fun guy

Molds are microscopic fungi that produce spores, which help them reproduce. They come in different sizes, shapes and colors. Each spore can grow into more fungus, which in turn can make millions of more spores. That means that once your house has mold, it can be very hard to get rid of it.

When you inhale mold spores, they sometimes get past the protections of the nose and throat to reach the lungs. Thousands of types of mold grow all around us. However, only a few dozen molds cause allergic reactions.

The score on spores

According to the American College of Allergy, Asthma and Immunology (ACAAI), about 10 percent of the U.S. population is allergic to mold. People with mold allergy can get:

  • Sneezing, nasal congestion
  • Coughing, sore throat
  • A runny nose, postnasal drip
  • Itchy, watery eyes
  • A skin rash
  • Inflamed sinuses

Some people also get allergy-related asthma. It makes them cough, wheeze and be short of breath.

To diagnose an allergy to mold or fungi, your doctor needs your complete medical history. If your doctor suspects you are allergic to mold, you might be asked to do a skin test.

The smell of a sick house

If your home has a musty-smelling odor, you might have a mold problem. Mold appears anywhere moisture levels are high and air flow is low, which means basements, kitchens, bathrooms—even your garage. Take a close look at the favorite hiding places for mold: house plants, the drip trays under your refrigerator, humidifiers, garbage cans, shower curtains, drains and around faucets.

Can't look inside? Take a whiff: Old upholstered furniture, foam rubber pillows, sleeping bags and mattresses are sometimes full of mold, especially if they've been in storage. Since your ability to smell mold drops rapidly, it's best to sniff for the stuff after you've been away for a while.

Mold can grow almost anywhere if the conditions are right—behind walls, on the grout in bathtubs and showers, in carpet pads and in the carpet itself. New houses are not even immune. In fact, drafty old houses can provide better ventilation than newer, more airtight homes. When the weather is good, be sure to open your windows and let in some fresh air.

Make mold a memory

If household mold is making you miserable, cleaning out the mold and getting rid of ways for it to come back are your top priorities. If you have a serious mold problem, get in touch with a certified mold inspector and a mold remediation company (a professional mold remover). If you try to get rid the moldy areas of your home on your own, you could spread spores all over the house. Plus, there might be mold lurking behind walls or under floors. An expert mold inspector can test to see what types of mold your house has and how much mold is in it.

To prevent mold from taking hold in the first place, follow these basic steps:

  • Bring down the humidity. Keep the relative humidity in your home at around 35 to 50 percent. If you need to, use a dehumidifier. Keep your basement as dry as you can.
  • Keep it clean. Scrub the kitchen and bathroom regularly to prevent mold in moist areas. Consider removing any bathroom carpeting. Scour garbage cans regularly.
  • Run a tight ship. Quickly repair any plumbing or roof leaks, and clean or replace water-damaged woodwork, carpeting or furniture.
  • Get more air. Use an exhaust fan to remove water vapor from your bathroom (especially while showering) and from your kitchen while boiling water or running the dishwasher. Make sure your home has proper air circulation.
  • Throw it out. Get rid of musty old books, newspapers, clothes or bedding.

If you see a small spot of mold, don't panic—grab some bleach and get busy. (Be sure to use proper protection such as rubber gloves, eye protection and a face mask.)

However, if you're feeling sick or the moldy area is larger than just a spot, have yourself tested for mold allergies and get your house or apartment tested for spores. It's the best way to ensure that your home is keeping you safe—not making you sick.

Published on May 15, 2008; updated on May 20, 2014.