There's no treatment for physical urticaria and "we still don't have a really good clue as to how [the hives] come about," said Casale. "These syndromes aren't extremely common and they're very difficult to study."
Normally we're pretty careful about the kinds of things we let touch our faces, but how often has that concern come to mind when that thing is your cell phone?
In recent years, dermatologists have begun to see an increasing number of contact dermatitis patients who are allergic to their cell phones, or more specifically the nickel in their cell phones.
"Some people are extremely nickel-sensitive," said Dr. Lionel Bercovitch, a professor of dermatology at Brown Medical School.
Nickel is a metal that's used in a wide variety of products, including jewelry, belt buckles and watch bands. It's the most common cause of contact dermatitis in the developed world.
The symptoms of a nickel reaction range from redness to a more obvious rash, even blisters. Bercovitch suspects some cases involving cell phones are not being reported because the symptoms are being confused with facial eczema.
"My guess is that it's probably more common than we think, but it's just not widely recognized," he said.
Not all cell phones contain nickel. In an attempt to get an idea of how many phones might have the metal, Bercovitch tested 22 models and published the results in the Canadian Medical Association Journal in January 2008.
Ten devices were positive for the metal. In some, the nickel showed up around the menu buttons. In others, it appeared near the decorative logos, around the edge of the screen or on a part of the handset where paint was chipped.
"I think you need the perfect storm of somebody who's allergic to nickel in the first place, and somebody who uses the cell phone a lot, and a cell phone that has an exposed nickel area," said Bercovitch.
The unexpected allergic reactions to nickel don't stop at cell phones.
"We're starting to see people who have rashes in other places because of the unexpected content of nickel in those items," said Dr. Sharon Jacob, assistant professor of medicine and pediatrics at the University of California at San Diego.
Jacob notes she's cared for children who've developed rashes on the back of their legs due to contact with nickel-plated studs on the seats of their classroom chairs.
"You can get blisters, you can get scarring," said Jacob. "We're seeing children as young as 4, and they're becoming scarred from this."
Other patients have more challenging cases to solve. Jacob once treated a girl who developed severe lip dermatitis after playing a flute containing the metal.
One problem with diagnosing the allergy is the rash could come a week after contact with nickel, so not everyone associates the symptoms with the potentially problematic object, said Jacob.
The number of allergy patients testing positive for a nickel reaction is on the rise in the United States. Many clinicians have attributed the increase, especially in men, to a growing number of ear and other piercings.
About 19 percent of patients with allergic dermatitis are sensitized to nickel, reported the North American Contact Dermatitis Group in data from 2003-2004. The number of such patients was much smaller in 1985-1990 -- about 11 percent.