How do you know when mold has arrived? That’s easy: you’ll smell the — how to put this? — the airborne end products of its digestive processes. That’s right, mold farts. “Every time you smell that musty odor, that mold smell, that’s what you’re breathing in,” said David Denning,principal investigator at the Manchester Fungal Infection Group and a professor at the University of Manchester, in England.For most, these stop when you leave the moldy room. But experts estimate that between 5 and 10 percent of the population are more sensitive than others. “In an environment that’s colonized by fungus, you’re also going to be inhaling those spores every day and you may potentially become sensitized to them,” said Elaine Bignell, Ph.D., who co-directs the Manchester Fungal Infection Group.