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.
How does one become sensitized to nickel? As Jacob explains it, for some people the intimate contact between the skin and the nickel used in earrings and ear posts can do the trick.
"In general, the first time you're in contact with nickel, you don't get a rash," said Jacob. But your immune system remembers the metal and eventually, after more exposure, you reach an "elicitation threshold" when "your skin is primed to react."
Jacob says she wants the American Academy of Dermatology to help push for regulations to limit the amount of nickel in products with prolonged skin contact, just as was done in Europe in the early '90s.
For thousands of years, people in North Africa, the Middle East and South Asia have decorated their bodies with henna, but in recent decades, adulterations in the dye used for these temporary tattoos have resulted in painful allergic reactions.
Henna is a normally reddish-brown or greenish-brown vegetable coloring derived from lawsone, an ingredient found in the leaves of the henna shrub. Normal henna rarely causes allergic contact dermatitis, but darker henna containing an added chemical also found in hair dye called p-phenylenediamine, or PPD, can instigate severe skin problems and additional allergies.
In some cases, the tattooed skin of those who are allergic to PPD will swell and blister, with the contours of the bumpy skin conforming to the shape of the original tattoo.
"When they add the black hair dye at significant concentrations … we're seeing people with blistering and scarring to it," said Jacob.
It's not unusual for people who react to black henna to also react to hair dye, sometimes as a result of the black henna encounter.
While PPD in small amounts is still allowed in hair dyes, it has been banned from skin products in the United States since 1938. Still, henna artists hoping to capitalize on the popularity of the black coloring can mix the dangerous paste on their own.