Complex sentence: Unnecessary or overuse of a humidifier can raise the relative humidity to high levels, promoting the growth of dust mites and mold and can also cause Hypersensitivity pneumonitis (humidifier lung).
Split into simpler sentences: Unnecessary or overuse of a humidifier can raise the relative humidity to high levels, promoting the growth of dust mites and mold. Can also cause Hypersensitivity pneumonitis (humidifier lung).