CRH and irritable bowel syndrome: Possible triggers for mast cell activation include, next to the aforementioned (food allergen-specific) IgE, a broad range of nonimmune signals such as substance P, nerve growth factor, calcitonin gene-related peptide (CGRP).33 Because stress is an important trigger for IBS-associated complaints, the stress hormone corticotropin releasing factor (CRF) received a lot of attention.