Dirty humidifiers can cause problems for people with asthma and allergies, says Mayo Clinic. However, the increased humidity may ease breathing in individuals who have asthma as long as the humidifier and filter are clean.
Dirty filters and reservoirs in humidifiers quickly breed mold and bacteria, which not only cause problems for people who suffer from asthma and allergies but healthy people as well, states Mayo Clinic. Dirty humidifiers can trigger lung infections and flu-like symptoms when contaminated steam or mist is released into the air. Steam vaporizers or evaporators are less likely to release allergens into the air than cool-mist humidifiers.