Although the underlying mechanism remains to be elucidated, one possible hypothesis is that patients with histamine-related conditions, such as seasonal allergic rhinitis, allergic asthma, or intestinal disorders (including Crohn’s disease and ulcerative colitis), who are known to have higher plasma histamine concentrations than healthy individuals, may be more susceptible to ABCP-related skin eruptions [19, 20]. This evidence concerns the gene ABCG2 and ulcerative colitis.