Indoor humidity refers to the amount of moisture in the air inside your home or office building. Maintaining proper indoor humidity levels is important for health and comfort. Very low humidity can cause irritation of the throat, skin, eyes and nasal passages. On the other hand, very high humidity provides a fertile environment for biological contaminants like mold, dust mites and bacteria which can cause or worsen respiratory issues. So what is considered “high” indoor humidity and at what point does it start to negatively impact health? Let’s review the evidence.
What is considered high indoor humidity?
The ideal indoor humidity level is between 30-50% according to most experts. The Environmental Protection Agency (EPA) recommends keeping indoor humidity below 60% to help limit mold growth.
| Indoor Humidity Level | Comfort and Health Impact |
|---|---|
| Below 30% | Dry air, irritation of throat, eyes, skin and nasal passages |
| 30-50% | Ideal comfort range |
| 50-60% | Humid, increased dust mites and mold growth possible |
| Above 60% | Very humid, high risk of mold growth and bacterial contamination |
Most people find humidity levels above 60% to be uncomfortably muggy. Humidity levels above 70% are associated with health risks if sustained for long periods.
How does high humidity impact health?
Prolonged exposure to high humidity indoors can potentially cause or worsen certain health issues:
Increased growth of mold, bacteria and dust mites
When indoor humidity rises above 60%, it provides ideal conditions for mold, bacteria, dust mites, cockroaches and other pests to thrive.
Mold exposure can trigger allergic reactions and asthma symptoms in sensitive individuals. Some molds produce allergenic proteins called mycotoxins that can cause respiratory distress when inhaled. Mold spores can also exacerbate pre-existing respiratory conditions like chronic obstructive pulmonary disease (COPD).
Bacteria and dust mites also proliferate in humid environments. Dust mites are a major indoor allergen and exposure can cause perennial allergic rhinitis and asthma attacks. Bacteria like streptococcus and staphylococcus can cause infectious illnesses.
Increased risk of Legionnaire’s disease
Legionnaire’s disease is a severe form of pneumonia caused by Legionella bacteria. It thrives in warm, stagnant water environments like cooling towers, hot tubs and plumbing systems.
When water droplets containing Legionella become aerosolized, people can inhale the bacteria. High humidity indoors can increase condensation and dispersal of contaminated water from cooling systems, thereby raising Legionnaire’s risk. Maintaining indoor humidity below 60% helps limit proliferation of Legionella bacteria.
Respiratory infections
Indoor humidity over 70% provides favorable conditions for various viruses, bacteria and fungi to survive and spread. Very humid air enables pathogens to remain suspended longer after being sneezed or coughed out by infected individuals.
Prolonged exposure to extremely humid conditions can potentially increase your risk of contracting illnesses like pneumonia, bronchitis, colds and flu from other people. However, the exact risk increase is difficult to quantify. Good hand hygiene and ventilation remain the best preventive measures.
Allergic reactions and asthma
In addition to mold allergies, some people have allergic sensitivities to dust mites and cockroaches which flourish in humid environments. Exposure can cause inflammatory reactions like coughing, sneezing, runny nose, respiratory distress, skin rashes or headaches in allergic individuals. People with asthma may experience acute shortness of breath and wheezing when exposed to these allergens.
Impact on COPD symptoms
For those with chronic obstructive pulmonary disease (COPD), high humidity indoors can exacerbate respiratory symptoms. COPD causes narrowing of the airways and mucus build-up, making breathing difficult. High humidity further aggravates this by slowing down natural evaporation of mucus from respiratory tracts. Stagnant mucus provides an environment for infections to develop, which can worsen COPD flares.
Increased condensation and drips
Excessive moisture indoors results in water vapor condensing on cooler surfaces like walls, windows and pipes. Persistent condensation can lead to mold growth and drips that damage ceilings, wallpaper and paint. This also provides additional hydration for pests like termites and cockroaches. Condensation drips may also ruin furniture, electronics or other possessions.
Discomfort from heat and stuffiness
Humidity above 70% prevents efficient evaporative cooling from our bodies, causing many people to feel uncomfortably warm or clammy. High humidity also traps indoor air pollutants and odors creating a stale, stuffy sensation. This can potentially raise stress levels and worsen mood.
Who is most affected by high humidity?
Certain populations are more susceptible to health issues linked to humid conditions:
– Infants and young children
– Older adults
– Pregnant women
– People with respiratory conditions like allergies, asthma, COPD
– People with weakened immune systems
Infants, children and older adults tend to spend more time indoors in one location so their exposure to allergens and pathogens may be higher. COPD patients have greater sensitivity due to their compromised respiratory function. Individuals taking immunosuppressant drugs or those with illnesses like HIV/AIDS are more vulnerable to infectious microbes that propagate in humid conditions.
However, young and healthy people may also experience health issues if indoor humidity remains at very high levels for prolonged periods. Headaches, lethargy, throat irritation and wheezing are common physical responses to extremely humid conditions, even in those without respiratory disorders.
Tips to control high indoor humidity
Here are some steps you can take to reduce excess moisture and limit humidity levels indoors:
Use air conditioners and dehumidifiers
Air conditioners reduce air moisture as they cool, so running them regularly helps control indoor humidity. If you don’t have central AC, use window air conditioning units or portable dehumidifiers in humid areas like basements or bathrooms. Make sure equipment is properly sized for the space.
Increase ventilation
Open windows and use fans to improve air circulation and ventilation. This allows fresh dry air to enter and stale moist air to escape. Make sure to use exhaust fans when bathing or cooking.
Check for leaks or drips
Inspect roof and plumbing for water leaks that need repairing. Insulate water pipes to reduce condensation drips. Empty and clean drip trays under refrigerators, AC units or dehumidifiers regularly. Discard excess moisture collected in dehumidifiers.
Limit indoor humidity sources
Avoid activities that release large amounts of moisture like laundry drying, long hot showers, boiling pots of water or using humidifiers. If needed, run these in short intervals with exhaust fans on.
Maintain air flow around belongings
Don’t overstuff closets or storage areas. Allow space between furniture and walls. Open closet and cabinet doors regularly to ventilate. These measures prevent moisture build up on belongings.
Use moisture absorbing products
Place bowls of baking soda or calcium chloride in humid areas to absorb excess moisture. Silica gel packets can be used in closets and cabinets.
Keep indoor temperature moderately cool
Cooler air holds less moisture. Maintain indoor temperature at the lowest comfortable setting to limit humidity levels.
Conclusion
Indoor humidity consistently above 60% can potentially cause or aggravate various health issues, especially among vulnerable populations like infants, older adults and those with respiratory diseases.
However, simply having periods of high humidity does not always directly translate to illness. Factors like duration of exposure, ventilation and presence of moisture sources also play a role.
Practicing proper moisture control, ventilation and prompt leak repairs helps limit mold, bacteria and pests. This reduces related health risks like allergies, infections and asthma exacerbations.
Keeping indoor humidity within the ideal 30-50% range as often as possible is recommended for a healthy living environment. Using dehumidifiers when required and taking steps to minimize excessive dampness indoors can help prevent humidity-related health issues.