Molds and fungi are naturally-occurring organisms that can be found everywhere, both indoors and out. Humans do not live in a mold-free environment, nor would we want to. Molds are a necessary part of our natural environment.
Problems occur, however, when conditions indoors allow for excessive mold growth. The primary culprit for this excessive growth is excess moisture. No excess moisture = no excess mold growth. Maintaining your home or building to prevent excess moisture and properly fixing moisture problems when they do occur are the keys to preventing both structural damage to the building as well as the risk of health problems to those living and working in the building.
The internet offers thousands of sites on mold and the effect of mold on health. The links contained on this site offer highly credible, well-researched, scientifically-based guidance.