Rye contains proteins called secalins that are closely related to wheat's trigger proteins. The immune system treats them as essentially the same thing, which is why about 88% of adults who react to wheat also show immune reactivity to rye. In practical terms, if wheat triggers eczema, rye should be assumed to as well until proven otherwise.

Many 'rye' breads are actually mostly wheat flour with some rye added, delivering both triggers. True 100% rye bread, especially sourdough-fermented rye, has had more of its problematic proteins broken down during fermentation and may be somewhat better tolerated, though it should still be approached with caution.