Are humidifiers safe to use?

Humidifier Safety Guidelines

Humidifiers can be safe to use when proper maintenance protocols are followed, but they pose significant infection risks if not properly maintained, particularly large-volume and ultrasonic models that generate aerosols. 1

Types of Humidifiers and Associated Risks

• Large-volume room-air humidifiers (>500cc) that create aerosols (using Venturi principle, ultrasound, or spinning disk) pose the greatest risk for pneumonia due to the large amount of aerosols they generate 1
• These large reservoirs can become contaminated by healthcare workers' hands, unsterile humidification fluid, or inadequate sterilization between uses 1
• Ultrasonic humidifiers can lead to exponential increases in bacterial aerosol concentrations, particularly in respiratory-sized particles (≤1.1 μm), with concentrations exceeding 1000 CFU/m³ within one week at 70% relative humidity 2
• Portable ultrasonic humidifiers can substantially alter indoor bioaerosol communities, promoting pathogenic bacteria like Pseudomonas, Brevundimonas, Acinetobacter, and Legionella species 2
• Wall humidifiers used for oxygen therapy should be maintained according to manufacturers' instructions 1

Safety Precautions for Humidifier Use

Water Quality Requirements

• For bubbling humidifiers: Use only sterile water 1
• For wick humidifiers: Use sterile, distilled, or tap water 1
• For large-volume nebulizers/humidifiers: Fill only with sterile water 1
• For ultrasonic humidifiers: A 2011 case report documented significant inhalational lung injury in an infant from mineral dust ("white dust") dispersed by an ultrasonic home humidifier 3

Cleaning and Maintenance

• Large-volume room-air humidifiers must be sterilized or subjected to high-level disinfection at least daily 1
• Between uses on different patients: Change tubing, including nasal prongs or masks used to deliver oxygen 1
• Reusable humidifiers: Show high rates of microbial contamination (50-83%) after 5 days of use, with common pathogens including Pseudomonas aeruginosa and Staphylococcus aureus 4
• Disposable humidifiers: Show significantly lower contamination rates and are preferred in healthcare settings 4

Specific Recommendations for Home Use

• Avoid long-term and excessive humidification (RH ≥ 70%) 2
• Clean ultrasonic humidifiers weekly to minimize exposure risks 2
• Follow manufacturer's instructions for maintenance and cleaning 1
• Consider using convection-type humidifiers which produce water vapor but do not aerosolize water, potentially reducing infection risk 5

Special Considerations

• For patients with tracheostomies: Passive humidifiers (heat and moisture exchangers) may be used, but they add resistance to breathing and dead space 1
• For patients using speaking valves: Passive humidifiers will not work because no heat or moisture is captured for the next inspiration 1
• Essential oils in humidifiers/vaporizers: Can increase risk of exogenous lipoid pneumonia 6

Common Pitfalls

• Inadequate cleaning: Bacteria can multiply to dangerous levels within 24 hours in contaminated reservoirs 1
• Using tap water in ultrasonic humidifiers: May lead to dispersal of mineral dust and potential lung injury 3
• Excessive humidification: Levels at or above 70% RH can lead to rapid bacterial proliferation 2
• Assuming all humidifiers carry equal risk: Different technologies have different risk profiles; ultrasonic and large-volume aerosol-generating devices pose the highest risk 1, 2