Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle (e.g., dust) levels in homes increase because of dirty air ducts. This is because much of the dirt in air ducts adheres to duct surfaces...be aware that although a substance may look like mold, a positive determination of whether it is mold or not can be made only by an expert and may require laboratory analysis for final confirmation. For about $50, some microbiology laboratories can tell you ...EPA does not recommend that the air ducts be cleaned routinely, but only as needed. If a service provider or advertiser asserts that EPA recommends routine duct cleaning or makes claims about its health benefits, you should ...