Many building supply stores sell mold-testing kits. The kit contains a flat plastic dish that you fill with nutrients for mold to grow. You set the dish out open for a limited period of time before putting the cover back on the dish. You can then either watch the dish to see what grows, or send the dish to a lab for analysis. This type of testing can be useful under certain circumstances. If you put the dish in your basement, for example, and then find that 20 identical colonies of blue-green or black mold grew in the dish, you know you have a mold problem.

But in most cases, the results obtained from these mold-testing kits can be misleading. If you put the dish in a room with an open window or slider, chances are that some mold will grow because mold spores came inside from the exterior. Clients have called to tell me that instead of leaving the dish open for an hour as directed, they left it exposed for a day in a room with an open window. I’d have been pretty surprised if, under those circumstances, mold hadn’t grown in the dish! In addition, these tests indicate the presence of only living mold spores. Most mold spores from indoor sources are dead, but dead spores can still cause health symptoms. And if you have a carpet in your house that contains moldy dust, and you don’t walk across that carpet while the dish is open, you may get a false “no mold present” result.

Finally, these mold-testing kits do not accurately report the extent of your exposure or how your health may be affected. If you are concerned about health symptoms that may be caused by mold, see your physician, rather than believing some report from a do-it-yourself mold testing kit that identifies the different kinds of colonies found and then lists illnesses that are supposedly associated with exposure to them.

If you want to understand why and where mold grows, learn how to get rid of it and prevent it from returning, buy a copy of The Mold Survival Guide: For Your Home and for Your Health, Jeffrey C. May and Connie L. May (2004). Jeff May is also author of My House is Killing Me! The Home Guide for Families with Allergies and Asthma (2001) and co-author of Jeff May’s Healthy Home Tips (2008). All three books are published by The Johns Hopkins University Press and are available on amazon.com.