Mold around a toilet can form from high humidity, poor ventilation, or condensation on cold porcelain surfaces. In bathrooms where warm, moist air meets cool toilet tanks — a common scenario during colder months — condensation can collect and drip unnoticed. When combined with minor plumbing issues, this moisture buildup can lead to mold behind the toilet, under the tank, or around the base. A plumbing inspection can help determine whether moisture is coming from a leak, condensation, or both.
