Positively identifying a caffeine allergy requires an allergy test; however, after consuming a food or beverage containing caffeine, an individual may experience some signs of an allergic reaction or intolerance, says About.com. These symptoms include insomnia, nausea, diarrhea, headaches, hives and fast heart rate.
The symptoms may occur immediately or within a few hours after consuming caffeine, but this does not always mean a caffeine allergy is present. The symptoms may be due to a non-allergic food intolerance to caffeine. Avoiding foods and beverages that contain caffeine may be the best way to alleviate this allergy. According to About.com, some additional treatments may include antihistamines and epinephrine.