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Do you sometimes find yourself "zoning out" next to a gas stove or a fireplace? Does a stuffy room make your thinking fuzzy? The problem may be carbon dioxide.

Nearly every home nowadays has smoke and carbon monoxide detectors. Smoke detectors, which tend to be fussy and easily set off, warn us of fires. Carbon monoxide detectors warn us of potentially deadly gases from trapped gases from automobiles, gas stoves for heating and cooking, and generators. Both smoke detectors and carbon monoxide detectors are usually legally required in apartments, and are a must for every family. Another indoor air danger lurks in homes and offices, however. It's carbon dioxide, CO2.

CO2 Toxicity May Cause Subtle Symptoms

Keeping a balance between oxygen and carbon dioxide is essential for human health. We breathe in oxygen that every cell in our bodies uses to make energy. Carbon dioxide is formed as a waste product. Just as too much atmospheric carbon dioxide can cause acidification of the oceans, too much carbon dioxide in the bloodstream can cause acidification of the human body. The resulting condition, called hypercapnia, can lead to drowsiness, sleepiness, and fuzzy thinking, followed by headaches, flushed skin, rapid breathing, rapid heart rate, muscle spasms, twitches, seizures, and eventually death.

CO2 Toxicity Is More Common Than Doctors Used to Think

Hypercapnia in outdoor air is very rare. A lake in central Africa "burped" a huge amount of carbon dioxide that killed thousands of people several decades ago, but it's almost unheard of for people to suffer CO2 poisoning outdoors. Hypercapnia indoors was thought to be rare, too, usually due to an industrial accident or the inappropriate use of dry ice, which is frozen carbon dioxide that turns into a gas (with fog) at temperatures below -100 degrees F. When doctors saw hypercapnia, it was usually due to medical conditions that interfere with breathing, such as brainstem lesions, asthma, chronic obstructive pulmonary disease (COPD), asthma, or sleep apnea.  CO2 poisoning wasn't something thought of as occurring on a daily basis.

Recent scientific research has changed that idea. In 2012, researchers at the Upstate Medical Medical University of the State University of New York and the  Lawrence Berkeley National Laboratory in California published the results of studies of workers exposed to high CO2 levels. They had volunteers do management tasks in an office-like chamber into which they could inject varying levels of pure carbon dioxide. The usual level of CO2 in air is about 400 parts per million. The researchers had the volunteers perform tasks for 2-1/2 hours at  CO2 levels of 600 parts per million (a typical CO2 concentration for indoor air), 1500 parts per million, and 2500 parts per million. 

Not surprisingly, the authors found that the higher the CO2 levels, the more thinking was affected. In particular, the ability to take initiative was drastically reduced at higher CO2 levels. The volunteers were still able to take in information, but they were not capable of taking leadership roles. They were compliant and unimaginative, one measure of independently initiated actions falling by over 90 percent.

High CO2 levels, of course, occur in classrooms. The same researchers noted that 21 percent of school classrooms in Texas have CO2 levels over 3,000 parts per million, a level at which independent thinking is difficult.

Continue reading after recommendations

  • Allen JG, MacNaughton P, Satish U, Santanam S, Vallarino J, Spengler JD. Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments. Environ Health Perspect. 2015 Oct 26. [Epub ahead of print] PMID: 26502459.
  • Satish U, Mendell MJ, Shekhar K, Hotchi T, Sullivan D, Streufert S, Fisk WJ. Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance. Environ Health Perspect. 2012 Dec.120(12):1671-7. doi: 10.1289/ehp.1104789. Epub 2012 Sep 20. PMID: 23008272.
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