The answer to 'why is my grout moldy' is that grout is a porous material that can easily trap moisture, which creates an ideal environment for mold growth. Common causes of moldy grout include high humidity, poor ventilation, water leaks, and improper cleaning or sealing of the grout.
Symptoms of moldy grout include discoloration, a musty odor, and visible mold growth. If the mold issue is not addressed, it can spread to the surrounding tile, walls, or floors and cause more extensive damage.