What factor is crucial for mold to grow indoors?

Mold growth indoors is primarily dependent on the presence of moisture. Mold spores are ubiquitous in the environment, and while they can be found in both outdoor and indoor settings, they require specific conditions to thrive. One of the most critical factors is moisture, which can come from various sources such as leaks, humidity, condensation, or poor ventilation.

When the relative humidity in a space rises above about 60%, or if there are any water-damaged materials present, it creates an ideal environment for mold to grow. Without adequate moisture, mold spores cannot germinate and proliferate, even if other conditions appear favorable.

Other factors, like temperature and air circulation, can influence mold growth, but they do not initiate it on their own. For example, while high temperatures can support mold growth, it is the moisture that serves as the fundamental requirement. Therefore, the presence of moisture is the primary concern when preventing mold development indoors.