Swimming in cold water is the most common cause of a severe reaction. This can cause a massive release of histamine resulting in low blood pressure,
fainting, shock, and even death. This allergic response can take several forms, from rashes to wheezing, hives, swelling and redness.
Cold urticaria is diagnosed by holding an ice cube against the skin of the forearm for 1 to 5 minutes. A distinct hive should develop if a patient has cold urticaria.