Ways Indoor Humidity Impacts Health & Thermal Comfort

5 Ways Indoor Relative Humidity Impacts Health & Thermal Comfort

When the level of relative humidity is too low or too high, achieving indoor comfort is easier said than done. Low humidity levels cause issues, from joint stiffness and sinuses irritation to dry eyes and itchy skin and lower immune response. On the other hand, high humidity can cause negative health effects and discomfort due to reduced indoor air quality.

humidity level

Common Signs of High Relative Humidity

When the indoor relative humidity is too high, your house will generally feel warmer than it is. Here are the common signs of high humidity levels.

  • Foggy mirrors and windows
  • Moist, clammy indoor air
  • Musty, foul odor
  • Disturbed sleep
  • Chronic discomfort
  • Mold growth
  • Wet insulation
  • Rotting wood
  • Peeling wallpaper
  • Blistering paint
  • Dust mites

High humidity levels indoors produce muggy conditions that often result in lesser comfort. For instance, home occupants may experience a disruption to their sleeping patterns and asthma aggravation. Also, allergies and other respiratory issues may indicate high humidity levels indoors.

Ideal Range of Indoor Humidity

Experts recommend relative humidity for comfort and better health within a home is between approximately 40% to 60%. Maintaining a humidity level below 60% prevents mold and mildew growth and dust mite infestations and inhibits the spread of bacteria.

How Indoor Relative Humidity Impacts your Health and Thermal Comfort

The air quality inside your home can impact your health in many ways. The amount of humidity or water vapor in the air can be especially important. Here are different ways indoor humidity affects your health and comfort.

1. Condensation

Condensation is a common problem in most households, especially during the winter months. When warm, moist air meets a cold surface, water droplets can form. This can lead to dampness and mold growth, both of which can be damaging to your home. Remember, warm air and vapor are often generated from various human activities such as bathing, cooking, and more.

The relative humidity of the air plays a big role in how much condensation will occur. The higher the humidity, the more likely it is that water droplets will form. In general, you want to keep the relative humidity in your home below 60%.

2. Spread of Viruses

According to Joseph G. Allen, the director of Harvard University’s Healthy Buildings program, maintaining indoor relative humidity at 40% to 60% helps reduce virus transmission. Based on scientific evidence, dry air supports the movement of viruses in the air. If an infected patient coughs, breathes, talks, or sneezes, they emit tiny respiratory droplets into the indoor air.

Dry air, or low relative humidity levels, causes these droplets to easily evaporate quickly. This forms virus-carrying particles that have been shown to stay in the air for an extended period. Their smaller size isn’t caught by many furnace filters and these particles can stay in suspension for hours, even days.

One study showed that the influenza virus was more stable and infectious at low relative humidity levels (RH). This means that the virus can remain suspended in the air for longer periods of time and be easily inhaled by people in the same room. Another study showed that rhinoviruses (the cause of the common cold) are also more stable and infectious at low RH levels. These findings suggest that maintaining a higher indoor RH level can help to reduce the spread of respiratory viruses.

3. Fungi, Mold, and Bacteria Growth

Fungi, mold, and bacteria are all common types of microorganisms that can be found in indoor environments. All three thrive in moist conditions, and as the relative humidity levels rise, so does their growth. High humidity levels also provide an ideal environment for dust mites, which are known to cause asthma and other respiratory problems.

In addition to causing health problems, these microorganisms can also damage building materials and lead to musty odors. To prevent the growth of these organisms, it is important to keep indoor relative humidity levels below 60% but not below 30% to prevent excessive air dryness, according to the EPA. This can be done by using a dehumidifier or by increasing ventilation.

4. Thermal Comfort

Indoor relative humidity (RH) is related to indoor temperature and thus can have a significant impact on thermal comfort. Generally, the higher the RH, at typical room temperatures, the warmer the air feels. This is explained by scientists by dividing the air temperature into sensible and latent heat or what we know more commonly as the “humidex” in hot weather.

It is important to strike a balance, as too high of an RH can be uncomfortable and lead to condensation on surfaces. An RH of between 40-60% is considered ideal for thermal comfort and health. Of course, other factors, such as air temperature and clothing, also play a role in determining thermal comfort. But by keeping indoor RH at a comfortable level, you can help to ensure that your home is a comfortable and healthy place to be.

5. Sleep Quality

The quality of sleep can be affected by many factors, including the environment in which you sleep. One factor that is often overlooked is indoor relative humidity. This is the amount of water vapor present in the air, and it can have a significant impact on sleep quality. When the air is too dry, it can cause nasal congestion, mouth drying, and skin irritation.

On the other hand, if the air is too humid, it can create an uncomfortable sleeping environment.

The ideal relative humidity for sleeping is between 40 and 60 percent. By maintaining this level of humidity, you can help to help with a comfortable and uninterrupted night’s sleep.

Final Thoughts

Overall, it is important to maintain indoor relative humidity levels within a comfortable range for both health and thermal comfort. Monitoring the RH level can help avoid problems such as static electricity shocks, respiratory infections, mold growth, and musty odors. Taking into account the season and individual preferences can ensure that everyone enjoys a comfortable indoor environment.


How does indoor humidity affect health?

Although the human body is adapted to a wide range of environmental conditions, indoor humidity levels that are too high or too low can lead to a variety of problems. For example, excessively dry air can cause respiratory problems such as nosebleeds and bronchitis, while excessive moisture can lead to the growth of mold and dust mites, which can trigger allergies and asthma. In addition, indoor humidity levels that are out of balance can also cause skin irritations, headaches, and fatigue.

How humidity affects your thermal comfort?

Humidity is the measure of the water vapor content in the air and plays an important role in our thermal comfort. When the air is saturated with water vapor, we feel sticky and uncomfortable. This is because our bodies rely on evaporation to cool down, and when the air is already full of water vapor, there is nowhere for our sweat to go. On the other hand, very dry air can also be uncomfortable as it can lead to static electricity discharges and makes our mucous membranes dry out.