Inclusion Criteria:  history of SNAS (coexistence of typical cutaneous and gastrointestinal symptoms); positive Ni-patch test; clinical improvement of at least 70% from baseline after 4 weeks of low-Ni diet; positivity of a double-blind placebo-controlled oral Ni challenge (DBPCO).  Exclusion Criteria:  age < 18 years and >65 years; other organic gastrointestinal diseases, such as peptic ulcer, inflammatory bowel diseases, celiac disease, gastrointestinal infections, and small intestinal bacterial overgrowth; diabetes mellitus; hepatic, renal or cardiac dysfunction; thyroid disease or tumour; concomitant treatment with steroids and/or antihistamines in the previous 4 weeks; pregnancy and lactation; smoking, abuse of alcohol, coffee, tea, and cola intake; inability to give written informed consent.