A recent study has found that the difference between homes with mold problems and those without is qualitative, not quantitative.

According to Elliott Horner, laboratory director at Air Quality Sciences, in Atlanta, the study looked at “non-problem” buildings — structures without water difficulties or moisture damage — and found that in some cases there were actually more mold spores than in some houses characterized as “problem” homes. “There is no evidence for a numerical distinction between non-problem houses and ones with mold problems,” Horner said.

Outdoor molds — most likely carried in by wind — were almost always the most prevalent in samples from non-problem houses. Horner said that the report concluded that if two samples taken from a house each contain only sparse amounts of outdoor mold, “that would be consistent with there being an indoor source of molds.”