Humidity—the amount of moisture in the air—affects comfort, air quality, and even how other pollutants behave. Both too much and too little can cause problems.
The Ideal Range: 30-50%
Most sources recommend keeping indoor relative humidity between 30-50%. This range:
- Minimizes dust mite populations
- Discourages mold growth
- Keeps airways comfortable
- Reduces static electricity
- Protects wood furniture and floors
Problems with High Humidity (Above 50-60%)
Mold Growth
Mold thrives in humid environments. Bathrooms, kitchens, and areas with poor ventilation are common problem spots. Mold spores become airborne and can trigger reactions in sensitive individuals.
Dust Mites
Dust mites flourish in humid conditions. Keeping humidity below 50% significantly reduces their populations.
Musty Odors
High humidity encourages bacterial and fungal growth that causes musty smells.
Discomfort
Humid air feels warmer than dry air at the same temperature. This can make apartments feel stuffy and uncomfortable.
Problems with Low Humidity (Below 30%)
Respiratory Discomfort
Dry air can irritate airways, causing dry throat, nose, and eyes. Some people experience more respiratory symptoms in very dry air.
Increased Dust
Static electricity in dry air makes dust cling to surfaces and stay airborne longer.
Skin and Hair Effects
Dry air can affect skin and hair comfort, though this varies by individual.
Material Damage
Wood furniture, floors, and musical instruments can crack or warp in very dry conditions.
Measuring Humidity
A hygrometer measures relative humidity. Digital versions are inexpensive and reasonably accurate. Many air quality monitors also include humidity sensors.
Check readings in different rooms—bathrooms and kitchens often have higher humidity than bedrooms and living areas.
Reducing High Humidity
Ventilation
- Use exhaust fans during and after showers
- Run the kitchen exhaust when cooking
- Open windows when outdoor humidity is lower
Dehumidifiers
Remove moisture from air. Useful in chronically humid spaces or during humid seasons. Need emptying or drainage setup.
Air Conditioning
AC naturally dehumidifies as it cools. In humid climates, AC helps control moisture.
Behavior Changes
- Don't dry clothes indoors (adds moisture)
- Fix any water leaks promptly
- Use lids when cooking to reduce steam
Increasing Low Humidity
Humidifiers
Add moisture to dry air. Types include evaporative, ultrasonic, and steam humidifiers. Each has pros and cons regarding noise, energy use, and maintenance.
Maintenance Important
Humidifiers can become mold and bacteria sources if not cleaned regularly. Follow manufacturer cleaning instructions carefully.
Simple Methods
- Houseplants release some moisture (minor effect)
- Leaving bathroom door open after shower
- Water containers near heat sources (minimal effect)
Humidity and Air Purifiers
Air purifiers don't affect humidity—they filter particles but don't add or remove moisture. However:
- Some purifier-humidifier combos exist (maintenance-intensive)
- Very dry air can slightly affect filter longevity
- Humidity affects how dust behaves in the air
For most people, treating humidity and air filtration as separate concerns with separate devices is simpler and more effective.