Different environmental factors can have an effect on the development of asthma, as well as on its clinical
expression. The main sources of environmental pollution are the burning of fossil fuels in the combustion engines of
different means of transport, in industry and in heating, as well as the biomass used for cooking and heating. Also
contributing to this complex mixture is the dust generated by traffic on road surfaces, or substances arising from the
degradation of vehicle parts, such as brakes or tires. Among the most abundant components of air pollution in urban areas
are particulate matter, nitrogen dioxide, ozone and volatile organic compounds. Sulphur dioxide is particularly abundant
in industrial areas. Various mechanisms on how environmental contaminants could cause asthma have been considered.
One possibility could be the direct irritation of the airway mucosa. Another possible mechanism could be the combination
of the contaminants with various allergens, increasing the allergenic activity. It has also been observed that some
environmental contaminants trigger cell inflammation processes. Epigenetic mechanisms, such as hypermethylation of
DNA or acetylation of histones, were also described. It has been observed in animal models that a pre-existing
mitochondrial dysfunction increases bronchial inflammation after exposure to ragweed pollen extract. In conclusion, it
appears that there probably is a harmful effect by environmental contaminants on asthma, increasing both the severity and
the prevalence of the disease. But the persistence of some contradictions in the data seems to support the need to continue
research in this field, clarifying the magnitude of this effect, as well as the underlying mechanisms, which could help to
identify measures to reduce the harmful effects of this exposure.