The answer to 'why is my hardwood floor mildew' is that mildew can grow on hardwood floors due to excess moisture, poor ventilation, or a water leak. Mildew appears as a fuzzy, discolored growth and can cause damage to the wood over time if left untreated.
Common causes of mildew on hardwood floors include high humidity, leaks from plumbing or appliances, poor air circulation, and flooding or water damage. Symptoms include a musty odor, discoloration, and visible mildew growth. To address mildew, you'll need to identify and fix the underlying moisture issue, then clean and treat the affected area.