HRH1 and allergic disease: For example, nasal symptoms of an allergic reaction have previously been associated with an increase of the H1R mRNA in the nasal mucosa of patients (Kitamura et al., 2015), and it has been reported that the severity of AR symptoms is correlated with higher levels of H1R gene expression (Panliang, 1988; Mizuguchi et al., 2012; Mizuguchi et al., 2021).