The answer to 'why is my upholstery mildew' is that upholstery can develop mildew due to excess moisture, poor air circulation, and lack of cleaning. Mildew thrives in damp environments and can grow on fabric, leather, and other upholstery materials.
Common symptoms of upholstery mildew include a musty odor, visible discoloration or spotting, and a fuzzy or powdery growth on the surface. Mildew can cause damage to the upholstery and be a health hazard, so it's important to address the issue promptly.