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What is the ideal indoor humidity level in winter?
2026-02-27
Overview
The World Health Organization recommends that indoor humidity be maintained between 40% and 70% year-round. Humans will feel most comfortable in an environment with a relative humidity of 45% to 65%.
If the humidity is below 40%, it will cause indoor dryness, leading to dry skin, throat, and respiratory tract, easily triggering respiratory diseases such as asthma.
When the humidity is above 70%, people will feel stuffy and uncomfortable.
When the humidity is above 80%, it is considered excessively high, making it difficult for the body to dissipate heat, resulting in symptoms such as increased body temperature, rapid heartbeat, dizziness, and nausea.
If the humidity is below 40%, it will cause indoor dryness, leading to dry skin, throat, and respiratory tract, easily triggering respiratory diseases such as asthma.
When the humidity is above 70%, people will feel stuffy and uncomfortable.
When the humidity is above 80%, it is considered excessively high, making it difficult for the body to dissipate heat, resulting in symptoms such as increased body temperature, rapid heartbeat, dizziness, and nausea.
Air humidity affects the human body in two ways: directly and indirectly:
1. Direct effects: The impact of indoor humidity on certain physiological processes in the human body.
2. Indirect effects: Mainly occur through changes in the concentration of certain biological pollutants (such as dust mites, bacteria, fungi, and viruses) and non-biological pollutants (such as formaldehyde, radon, sulfur oxides, and nitrogen oxides) caused by relative humidity, thus indirectly affecting human health.
Why it will effect your life?
Reduced resistance of the human respiratory system:
In dry environments, the resistance of the human respiratory system decreases, making it easier to trigger or aggravate respiratory diseases. Research results indicate that when the relative humidity in the air is below 40%... When the air is dry, the mucous membranes of the upper respiratory tract, including the nose and lungs, lose a significant amount of moisture. This reduces elasticity, decreases mucus secretion, and slows the movement of cilia on the mucous membranes. Dust and bacteria easily adhere to the mucous membranes, leading to dry skin and respiratory tract, dry throat, nasal bleeding, and weakened respiratory defenses, making the body more susceptible to infections.
In dry environments, the resistance of the human respiratory system decreases, making it easier to trigger or aggravate respiratory diseases. Research results indicate that when the relative humidity in the air is below 40%... When the air is dry, the mucous membranes of the upper respiratory tract, including the nose and lungs, lose a significant amount of moisture. This reduces elasticity, decreases mucus secretion, and slows the movement of cilia on the mucous membranes. Dust and bacteria easily adhere to the mucous membranes, leading to dry skin and respiratory tract, dry throat, nasal bleeding, and weakened respiratory defenses, making the body more susceptible to infections.
For the skin:
Dry air dehydrates human epidermal cells and reduces sebum secretion, resulting in rough, wrinkled, and even cracked skin. Allergic dermatitis, itchy skin, and other allergic diseases are also related to dry air.
Dry air dehydrates human epidermal cells and reduces sebum secretion, resulting in rough, wrinkled, and even cracked skin. Allergic dermatitis, itchy skin, and other allergic diseases are also related to dry air.
Dust mites:
Research shows that the optimal conditions for dust mite growth are a temperature of 20-25℃ and a relative humidity of 70%-75%. When the indoor relative humidity is below 51%, dust mites will die from dehydration.
Research shows that the optimal conditions for dust mite growth are a temperature of 20-25℃ and a relative humidity of 70%-75%. When the indoor relative humidity is below 51%, dust mites will die from dehydration.
Microorganisms:
Canadian scholars Anthony V. Arundel et al., after considering various factors, recommended an optimal relative humidity range (as shown in the figure). Research shows that a relative humidity of 40-60% is optimal. This minimizes the total number of bacteria, germs, mold, and parasites in the environment. It reduces the likelihood of respiratory infections, allergies, asthma, and chemical reactions, while ensuring a certain level of ozone generation, thus purifying the air.
Canadian scholars Anthony V. Arundel et al., after considering various factors, recommended an optimal relative humidity range (as shown in the figure). Research shows that a relative humidity of 40-60% is optimal. This minimizes the total number of bacteria, germs, mold, and parasites in the environment. It reduces the likelihood of respiratory infections, allergies, asthma, and chemical reactions, while ensuring a certain level of ozone generation, thus purifying the air.
Formaldehyde:
A Finnish study of 46 apartments found that when relative humidity changed from 34% to 70%, the formaldehyde concentration in the air increased from 0.08 mg/m³ to [a higher level] within 24 hours. 0.20 mg/m³, indicating that indoor formaldehyde concentration is directly proportional to temperature and humidity.
A Finnish study of 46 apartments found that when relative humidity changed from 34% to 70%, the formaldehyde concentration in the air increased from 0.08 mg/m³ to [a higher level] within 24 hours. 0.20 mg/m³, indicating that indoor formaldehyde concentration is directly proportional to temperature and humidity.
Why is the air still humid even with HRV on?
HRV helps with Air Exchange, replacing humid air with drier air—but it still has limitations if you have single-pane windows or non-insulated aluminum fittings. Unlike a dehumidifier, an HRV is still limited by its ability to evaporate condensation into the air and then be expelled. If the house isn't warm, less moisture will be absorbed into the air, so less will be removed.
Check that the HRV is working properly and not clogged with old filters. If you really want to prevent humidification but can't afford to replace your windows, you can try placing a dehumidifier in the room and running it at night, and/or sealing the windows with 3M plastic insulation kits to reduce the ability of warm, humid air to reach the cold windows and condense and seep out.
Tip: Use a dehumidifier at night or apply window insulation film.
Tip: Use a dehumidifier at night or apply window insulation film.
FAQ
1. What is the ideal humidity?
40%–60% is the healthiest range. It minimizes germs and mold. To kill dust mites, keep it below 51%.
2. What if it’s too dry (<40%)?
Low humidity dries out your respiratory membranes and skin. This weakens your defense against bacteria, causing dry throats, nosebleeds, and asthma triggers.
3. What if it’s too humid (>70%)?
High humidity causes formaldehyde levels to double within 24 hours. It also makes it harder for your body to cool down, leading to dizziness and a rapid heartbeat.
4. Why is my home still damp with HRV?
HRV is for air exchange, not dedicated dehumidification. If your house is cold or has single-pane windows, moisture will condense before the HRV can remove it.