Can blue dye, such as fd&c blue no. 2, cause an allergic reaction such as swelling?

Possibly: I suspect the answer is yes. 11 patients with chronic, unexplained itchy skin rashes that responded to medication changes centered around avoidance of coloring agents, fd&c blue no. 1 (bright blue) and blue no. 2 (indigo carmine). Reactions to agents that color medications and foods may be more common than previously appreciated. This is from journal of drugs dermatol. 2013;12(1):99-102.