Study low humidity and the barrier function of the body

Brief summary

Preliminary information
Influenza-A viruses (IAV) cause infections all over the world which lead to half a million fatalities each year. These influenza outbreaks occur in temperate regions during the winter months. They peak between November and March in the northern hemisphere and between May and September in the southern hemisphere. These epidemics involve the following factors: temperature fluctuations, low air humidity, too many people indoors, lack of sunlight and associated vitamin D deficiency.

The detailed study by Akiko Iwasaki et al. shows once again* that excessively low humidity significantly increases susceptibility to influenza infections.
(*Lipsitch et al. 2010, 30-year study)

An excessively low humidity of 10–20% RH leads to a reduction of the self-cleaning mechanism of the respiratory tract, to a reduction of resistance against viruses and to a reduction of the functionality of the memory cells of the immune system. At a higher relative humidity (50% RH), the reduction effects do not occur.

Three immune barriers to protect against infections
Protection against a viral infection should be enabled by 3 barriers of the immune system. The first barrier consists of the mucous layer, the liquid layer on the mucous layer and the
cilia on the surface. They enable the immune system to fight off pathogens and particles entering via the respiratory tract. When the virus breaks through this first immune barrier,
interferon is released to activate genes that fight and block the viruses. If the virus succeeds in penetrating this congenital second layer of defense, as the third level,
the adaptive immune system is activated in order to trigger virus-specific immune responses of the memory cells using B cells and T cells.

These three barriers become ineffective if the humidity is too low (10–20% RH). The influenza virus breaks out. The severity of the illness worsens at 10–20% relative humidity regardless of the viral burden. In addition, the ability of cellular tissue to repair itself is inhibited.

Influenza disease shows a weaker course at 50% RH with lower fever and shorter duration.

Study by Dr Akiko Iwasaki

What influences air humidity in our immune system
Influence of air humidity on the intensity of the infection

Infected pulmonary alveoli at
10% air humidity
Infected pulmonary alveoli at
50% air humidity
Influence of air humidity on the repair activity of damaged cells

Repair activity of infected pulmonary alveoli at air humidity of 10%
Repair activity of infected pulmonary alveoli at air humidity of 50%
Repair activity of infected pulmonary alveoli at air humidity of 10%
Repair activity of infected pulmonary alveoli at air humidity of 50%
2 Questions for Dr. Akiko Iwasaki
How does balanced ambient air humidity affect people who are exposed to the flu virus?
What are the protective mechanisms of balanced air humidity?

We have known for decades that flu epidemics occur mainly in winter when central heating is used indoors. Possible reasons why people get sick with the flu during the winter are the subject of intense discussion. Explanations given for this seasonality include exposure to cold temperatures, low air humidity indoors or outdoors, gatherings of large groups of people in indoor areas with increased contact or droplet transmission and a reduction in the vitamin D level in healthy blood due to low exposure to sunlight.

Not only is it interesting from a theoretical viewpoint to understand the causes of the seasonal flu and therefore to know which measures can be applied in order to reduce the associated probability of illness and death. The topic is of enormous importance, as seasonal flu infections continue to increase and cause at least half a million deaths worldwide
each year. The provision of balanced air humidity is a protective measure which supports vaccination and can be used to save millions of human lives.

This study shows that dry ambient air intensifies the impacts of the flu. It was also proven that regulating the relative humidity at between 40 and 60% minimizes a viral infection and impedes the transmission process. This is the first study showing the physiological mechanisms behind the positive results that are achieved through balanced air humidity.


Original title: Low ambient humidity impairs barrier function and innate resistance against influenza infection

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Published: 13.05.2019

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