Views: 0 Author: Site Editor Publish Time: 2023-02-16 Origin: Site
People can easily distinguish the hot and cold of the environment they are in, but the level of air humidity cannot be clearly perceived. We have no immediate feedback on the moisture content of the air we inhale into our lungs or in contact with our skin or body.
However, air humidity can have a major impact on us and can cause damage if exposed to extreme environments for extended periods of time.
Dry air draws moisture from any source it comes in contact with, including our bodies. Moisture can evaporate from our eyes, skin, hair, nails, and other body surfaces. This dehydration can cause initial discomforts, such as sore eyes or contact lens irritation, but it can also lead to more serious symptoms, such as dry, itchy skin and dermatitis.
More seriously, it affects our breathing and immune system. When the relative humidity of the air we breathe is below 40%, the mucous membranes in the nose, throat, and bronchi become dry, and these elements play an important role in our body's defense against airborne pollutants such as viruses and bacteria.
These moist mucous membranes trap airborne particles before they enter our lungs. Tiny hairs called cilia transport these pollutants to the area of our throat, where they are either coughed up or swallowed and destroyed. This process is called mucociliary clearance.
When our mucous membranes dry out, this natural defense mechanism is suppressed, making us more susceptible to airborne viruses and bacteria.
Numerous studies and investigations have been conducted over the years to demonstrate how humidity affects the human body. Below is a summary of the studies, with notable examples illustrating the health benefits of maintaining an optimal humidity level.
Study: Physiological and subjective responses to lower relative humidity
Author: Sunwoo Y etc., 2006
Citation: Journal of Physical Anthropology, 2006 Jan;25(1):7-14
Methods: Sixteen healthy subjects were monitored under controlled conditions of 25°C and 10%RH, 30%RH and 50%RH. Subjects' physical conditions were monitored, including mucociliary clearance time, eye blink frequency, skin hydration, and transepidermal water loss. Subjects were also asked to make subjective judgments about temperature, dryness, and perception of comfort.
Summary of results: If the relative humidity is low, mucous membranes are adversely affected, and drying of the mucous membranes of the eyes and the stratum corneum (outer layer) of the skin leads to a decrease in the average temperature of the skin. Interestingly, when the humidity was lowered, the subjects felt the cold immediately, but not in the dry environment.
Study: Nasal mucociliary transport slows in healthy subjects when inhaling dry air
By Salah B etc., 1998
Citation: European Respiratory Journal, 1988 Oct;1(9):852-5
Methods: To assess the effect of inhalation of dry air on nasal clearance, 250 μg of saccharin was deposited in the nostrils of 11 healthy subjects while inhaling dry or room air. Swallow every 30 seconds and measure the time between precipitation and first perception of saccharin taste.
Summary of the Results: Inhalation of dry air leads to excessive dehydration of the nasal mucosa, which reduces nasal mucociliary clearance due to changes in rheological properties or nasal mucosal adhesiveness and/or slowed ciliary flapping.
Study: Study on Human Nasal Mucus Flow
By Ewert G, 1965
Citation: Otolaryngology Supplement, 1965;200: SUPPL 200:1-62
Method: After the powder particles are inserted into the nostrils of the subjects, observe how long it takes for the particles to move 2mm, and measure the mucus flow in the human nose at different humidity levels.
Summary of results: There is a relatively significant correlation between the average flow rate and the relative humidity of the ambient air. Optimum flow occurs at >70%RH and continues to decrease as humidity decreases.
Study: The Dichotomy of Relative Humidity to Indoor Air Quality
By Wolkoff P, Kjargaard SK, 2007
Cite: International Environment, 2007 Aug;33(6):850-7. Epub 2007 May 17
Methods: Various epidemiological, clinical and human exposure studies related to relative humidity were examined.
Summary of results: These studies suggest that lower relative humidity plays an important role in increasing reported eye irritation symptoms and altering the precorneal tear film. These effects may be exacerbated during the operation of the visual display unit. Relative humidity around 40% is better for the eyes and upper airways than below 30%.
- For our body and immune system, 40-60% is the optimal relative humidity range.
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