Acids Can Promote the Onset and Multimorbidity of Allergic and Nonallergic Airway Diseases

Inflammatory allergic and nonallergic respiratory pathologies often co-exist. The root cause is not clear. This paper demonstrates that it is ascribable to protons (H⁺) released into cells by exogenous and endogenous acids. The hypothesis of acids as the common cause stems from two considerations: a) it has long been known that exogenous acids present in air pollutants can induce the irritation of epithelial surfaces, particularly the airways, inflammation and bronchospasm; b) according to recent articles, endogenous acids, generated in cells by phospholipases, play a key role in the biochemical mechanisms of initiation and progression of allergic responses. Therefore, the intracellular acidification and consequent Ca²⁺ increase, induced by protons generated by either acid pollutants or endogenous phospholipases, may be the causal mechanism of the multimorbidity of these diseases, and environmental acidity may contribute to their spread.