Mold spores

What it means

Molds reproduce by releasing spores. EPA describes them as tiny, invisible to the naked eye, and floating through outdoor and indoor air. CDC adds that “there is always some mold around.” Spores come in through open doors, windows and heating and cooling systems, and ride in on clothes, shoes and pets.

A spore on a dry surface does nothing. EPA says mold may begin growing indoors when spores land on wet surfaces, and none of the many types of mold will grow without water or moisture.

Why it matters to your home

Because spores are everywhere, you cannot make a home spore-free, and a quote that promises to is a red flag. The goal of cleanup is to remove active growth and fix the water problem. EPA recommends drying wet materials within 24 to 48 hours so that, in most cases, mold will not grow, and keeping indoor humidity below 60%, ideally 30% to 50%. Spore counts also explain why air tests can be hard to read. EPA notes that samples show only a moment in time and that no federal limits exist for mold or spores. See our guide to mold prevention.