Air pollution
One possible source of PHM is the fine particulate matter component of air pollution from burning fossil fuels. In many studies, microbes are only identified to the genus level. Interestingly, studies of crude oil reveal diverse microbiotas, including at least some genera that are the same as those found in humans, such as Pseudomonas and Mycobacteria. It seems possible that some studies might fail to detect microbes originating from fossil fuels.
A recent study found the proportion of pathogenic species increased with air pollution levels associated with urbanization[14]. A study also found that there were changes in the pharyngeal microbiota following a severe air pollution event, including detection of 142 new genera in the pharynx[15]. Some of the microbes found in cigarette smoke also might be considered to be PHM and might play a role in tobacco-associated diseases.
A number of studies have linked fine particulate matter exposure to increased rates of allergic diseases[1]4, respiratory infections[16] and overall mortality[17]. Air pollution has been associated with evidence of stress effects as measured by blood pressure, heart rate, and heart rate variability.