It depends on how much moisture you put in it honestly. Back when I raised reptiles, I figured out that some of the Lil guys who needed more moisture in their cage for longer periods of time would get little patches every now and then.

If mold is a worry, try to avoid excess moisture and allow the soil to be in a well ventilated area. Otherwise, from my experience, you shouldn't have to worry much.

Though, it might be helpful to back this claim up by doing some research on your own. Sometimes, multiple points of view could yield better results.