After a 34-year-old man experienced a life-threatening allergic reaction after stepping out of a hot shower, doctors discovered a rare and serious condition that caused the reaction: The man was allergic to the now-cold air.

A hot shower leads to anaphylactic shock

Providers detailed the incident in a case report recently published in the Journal of Emergency Medicine. According to the case report, the man took a hot shower and, shortly after he stepped out the shower, he collapsed as a result of anaphylaxis. The man's family found him on the floor and called for paramedics. When the paramedics arrived, they gave the man oxygen and epinephrine before transporting him to the ED.

When he arrived at the ED, the man was sweating heavily and having trouble breathing, and he had hives all over his body. Providers admitted the man from the ED to the hospital's ICU.

The man's family informed his doctors that he had a history of being allergic to the cold, though up until that day, the worst symptom he had experienced was hives.

Doctors then performed an allergy test that involved rubbing an ice cube on the man's skin for five minutes and watching for hives to develop. The man did develop hives, and his providers diagnosed him with cold-induced urticaria—or hives—as well as anaphylaxis. His doctors concluded that the cold air the man stepped into when he got out of the hot shower likely caused his severe allergic reaction.

Providers treated the man with antihistamines and steroids while he was at the hospital, and the treatments helped him make a full recovery. Providers also prescribed the man an auto-injector of epinephrine to use if he experienced anaphylaxis in the future.

A rare and serious condition

It's unclear just how common cold-induced urticaria and anaphylaxis are, but cold allergies are believed to be rare. Typically, people with the condition only experience skin irritation, and not anaphylactic shock.

In addition, such reactions to the cold happen when allergic patients experience a sudden drop in temperature, such as when they're swimming in cold water. There also are some documented cases of reactions happening when cold intravenous fluids are given to a patient with a cold allergy.

The cause of the condition isn't known for certain, but in a study published in 2012 that involved 27 people from three different families, researchers discovered a mutation in a gene called PLGC2 that caused the immune cells of patients with a cold allergy to react differently to the cold compared with people who don't have the condition. The immune cells of patients with a cold allergy, when exposed to the cold, released histamine, which causes the body to become inflamed and can cause allergic reactions. Still, many with the condition have no known genetic cause, Forbes reports.

Ultimately, the authors of the case report wrote that providers should "be aware of the potential for cold anaphylaxis as it can change patient guidance and alter management." They also noted that the condition can "contribute to otherwise unclear and sudden decompensation in critically ill patients, as has been reported in cases of cold anaphylaxis induced by cold IV infusions" (Cara, Gizmodo, 11/2; Forster, Forbes, 11/5; Brevik/Zuckerman, The Journal of Emergency Medicine, 10/27).