Rye has been confirmed to contain proteins that trigger symptoms in people with celiac disease or gluten sensitivity.
Like wheat and barley, rye is a grain for which the United States Department of Agriculture (USDA) has developed standards. Unlike those other grains, however, there is only one edible species of rye and as a result only one USDA class for rye. USDA defines rye as any grain that consists of at least 50% common rye (Secale cereale L.) and no more than 10% of other grains for which it has established standards. In addition, the final product must contain at least 50% whole rye after sorting and cleaning.
A relatively hearty grain that thrives in cold climates, rye is commonly used in making bread (rye bread) and "mash" for distilled alcohol, particularly whiskey (or whisky, depending on the location of its origin) based on regional availability or for the somewhat unique flavor it imparts. Like barley, rye is not included among the FDA's eight major food allergens, meaning it is not required to be declared as such on food labels. However, rye is not as commonly used as is barley in making malt.
About the USDA's classification of rye ... Read the United States Standards for Rye [PDF]
About the different species of rye ... Take a look at the USDA profiles for cereal rye and others in the grass family
About rye and some of its common food uses ... Check out the USDA Commodity Image Gallery
About the 8 major food allergens ... Start with the FDA's guidance for consumers and food manufacturers