For a small, recurring patch, a thorough DIY approach can be attempted first. Use a dedicated hydrogen peroxide-based grout cleaner, not just bleach, which only removes surface color. Scrub deeply and ensure the area dries completely after each use. However, if the smell persists, the patches return quickly, or the growth is spreading beyond a small area, the moisture source is likely behind the tiles or within the wall.

In this case, professional assessment is recommended. They can use moisture meters to find the source of the problem—often a tiny cracked grout line or failing sealant letting water into the wall cavity. Remediation then involves fixing the leak, properly removing the contaminated material, and treating the area. Without addressing the hidden moisture, the mold will continue to return.