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How Humidity Affects Asthma


While cold, dry air is proven to increase asthma symptoms, not as much is known about hot, humid air, which also appears to worsen symptoms. A study by the University of Kentucky Medical Center sought to determine if this theory is true. Participants in the study included 6 asthma patients (ages 21-26), and 6 healthy patients (ages 19-46).

To test the effects of temperature and humidity, a breathing device was designed that produced a humidified mixture of gas at two different levels. One option was hot, humid air at 102 degrees Fahrenheit and approximately 80% humidity. The second option was cooler. drier air, at 72 degrees Fahrenheit and approximately 65% relative humidity. During testing, participants breathed in both types of air via the mouthpiece on the device. Immediately after using the device, airway resistance of the subjects was measured.

The effects of the hot air were compared to the room temperature air in all 12 participants. Results showed that the hot, humid air created an immediate increase in airway resistance plus coughing for asthma patients. Meanwhile, healthy patients had no response.

In a related experiment, the Children’s Hospital of Michigan also tried to determine how the increase in temperature and humidity affects asthma patients. Over 25,000 asthma-related visits at the hospital were analysed to see what roles temperature and humidity played. The hospital also controlled for factors such as airborne pollutants and seasonal allergens.

The results showed that on days when temperature and humidity were higher, asthma-related visits were also higher. For every 10% increase in humidity, there was one additional asthma patient in the emergency room compared to the 35 patient per day average. Additionally, every 10-degree rise in temperature related to 2 asthma patients over the daily average.

Both of these tests provide further proof that hot, humid air does seem to aggravate the symptoms of asthma. While the reasoning behind this is not fully understood, it is thought to be because of a group of nerves in the lungs called C-fibers. C-fibers are activated once the chest temperature is elevated above 102 degrees Fahrenheit. Once active, C-fibers create a coughing response. While more research needs to be done, knowing that hot air has negative effects is useful information for asthma sufferers.

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Sources:
Hayes , Don, et al. “Bronchoconstriction Triggered by Breathing Hot Humid Air in Patients with Asthma.” American Journal of Respiratory and Critical Care Medicine, University of Kentucky Medical Center, https://www.atsjournals.org/doi/abs/10.1164/rccm.201201-0088OC.
Nationwide Children's Hospital. "Why hot, humid air triggers symptoms in patients with mild asthma." ScienceDaily. ScienceDaily, 6 June 2012. .
“Temperature, Humidity and Your Asthma.” IQAir, IQ Air, https://www.iqair.com/blog/asthma-allergies/humidity-induced-asthma-symptoms.