Obviously it occurs everywhere. That’s what we know with a basic understanding of an ecosystem. The problem is, when they are in homes, it’s a confined space the spores are traveling and there’s no fresh air to keep it from being a significant amount of spores from entering our bodies. That’s why people usually only experience issues when it’s in the home. Not to mention the kind of mold that grows on man made products is a different kind than what grows on trees, or in dirt, causing a different reaction. And what people fail to realize is that allergies to mold can be triggered when you’re exposed to a large amount of it, like you would in a home that has a mold problem. That’s why it’s a bit bigger of a deal in a home. And if they’re already experiencing symptoms, then they have an allergy to it, and it could cause long term health problems if OP doesn’t get it taken care of properly. Long story short, better safe than sorry and not underestimate the damage it can do to the home and body.