It may sound like a mythical affliction: Being allergic to cold weather.
But an intriguing new study suggests an allergic response to cold is rare, but real – and potentially life-threatening.
The condition -- called cold urticarial – causes people to have allergic reactions that involve the release of chemicals called histamines. Hives appear on the skin minutes after exposure to cold air or water, or even walking into an air-conditioned room.

Investigators at the National Institutes of Health have identified a genetic mutation in three unrelated families that causes the rare immune disorder.
The study, published in the online edition of the New England Journal of Medicine, was led by Dr. Joshua Milner, in the Laboratory of Allergic Diseases at the National Institute of Allergy and Infectious Diseases.
The NIH study involved 27 people from three families who all suffered from an inherited form of cold urticarial. Researchers said it not only causes itchy, sometimes painful hives, but also episodes of fainting and, in certain cases, life-threatening reactions in response to cold temperatures. Sufferers are also more susceptible to developing autoimmune diseases.
"This is one of few examples in which the allergy symptom directed us to a genetic syndrome," says Milner. "In trying to understand the link between this group of conditions -- autoimmunity, chronic infections and cold urticaria -- we not only identified a disease-causing mutation but uncovered a unique and fascinating genetic mechanism at the crux of allergy, immune defense and self-tolerance."
Doctors can test for the condition by melting an ice cube on a patient's skin, then waiting to see whether hives begin. It can be treated with antihistamines.