The answer to 'why is my humidifier smells bad' is that a humidifier can develop bad odors due to bacteria, mold, or mineral buildup. This is a common issue that often occurs when the humidifier is not properly cleaned and maintained. The smells can range from a musty, stale odor to a rotten egg-like smell.
The main causes are letting water sit in the unit for too long, not changing the water frequently enough, or not thoroughly cleaning the humidifier on a regular basis. This allows bacteria, mold, and mineral deposits to accumulate, which then produce unpleasant smells. Neglecting to clean the humidifier is the most common reason for bad odors.