TORONTO - It could come from the metal on the back of your watch face, or your belt buckle's tendency to brush against the skin on your stomach. Or it could be the hair dye gooped onto your scalp when you go to have your roots touched up. Or the talc in the latex gloves you pull on at work.
It could even come from sitting on your sofa.
It is contact dermatitis, an irritating, sore and little understood skin problem that is suffered by many and caused by a plethora of different products and exposures.
It looks a bit like localized eczema — a scaly patch of pink or red skin on an arm where a watch would normally sit, or cracked and oozing eruptions on hands. Sometimes you might see swollen ears and a strip of angry red skin along the hairline.
The good news is the condition isn't life threatening and is generally pretty manageable — after you figure out what is triggering your skin's reaction.
Getting to the bottom of the problem can sometimes take Dr. House-like skills, with a dermatologist doing what amounts to a forensic investigation of the various items to which you are exposed every day to try to figure out if the culprit is your laundry detergent, your body lotion or a chemical you encounter at work.
"That's what's fun about it," says Dr. Sandy Skotnicki, a Toronto-based dermatologist who has a subspecialty in contact dermatitis.
"We are known as sort of detectives in the contact dermatitis realm. ... Sometimes you get crazy stuff."
She's seen a pig farmer who reacted to cobalt in pig feed. A veterinarian who developed a reaction to peppermint oil applied to cow udders. And a drug compounder whose face swelled up from a reaction to an antibiotic she was crushing to make into pills.
Then there was the woman who would get violent skin eruptions on the soles of her feet and the back of her thighs at work. She worked in a paint production plant and was allergic to a preservative used there. Skotnicki says it turned out a co-worker was surreptitiously spraying the woman's work shoes and the seat of her chair with the preservative.
Skotnicki didn't solve this mystery, but likes the example: Awhile back, people were showing up at dermatologists' offices with mysterious and extensive skin rashes. It turned out a lot of people are allergic to a preservative put into fabric used to upholster some couches — dimethyl fumarate.
More common cases involve hairdressers who develop an intolerance to hair dyes, mechanics who start reacting to preservatives in oil or nurses who develop reactions to a component of the gloves they wear at work.
Despite the wide range of causes and the fact that it's a pretty common condition, contact dermatitis is a sort of under-the-radar ailment.
"It is a condition that is not really known to the general public. Or, for that matter, to most doctors — unless they are dermatologists," says Dr. Mariusz Sapijaszko, an Edmonton-based dermatologist.
There are actually two types of the condition: contact irritant dermatitis and contact allergic dermatitis. The former is more common.
The names provide clues to the conditions and the differences between them. As it implies, contact means this is an external reaction to something which the skin touches.
It's in the same ballpark as allergies to foods or things we inhale like pollens or pet dander; it is caused by an immune system response. But the portion of the immune system that kicks into action with contact dermatitis is not identical to the part that delivers the runny nose symptoms of hay fever or the anaphylactic shock induced by a shellfish allergy.
Irritant dermatitis is caused by persistent exposures to something which irritates an individual's skin; that something can differ from person to person. It could be fragrances in body lotions or creams, or chemical components in cosmetics or solvents.
The solution is to figure out the source of the problem and dial back the exposure.
"If you have a strong soap and you wash your hands frequently or your body, you may develop contact irritant dermatitis to that soap. You're not allergic to the soap. You just have to use it less or less often and you'll be fine," Sapijaszko explains.
Contact allergic dermatitis is trickier. That's where a person develops an allergy that leads to skin eruptions. Nickel, which is a common component in costume jewelry, is a frequent culprit here. Inexpensive jewelry can trigger rashes; so too can metal snaps on shirts.
Hair dyes, henna and even the inks used in tattoos fall into this category. Developing an allergy to the ink in tattoos presents a real challenge, says Sapijaszko, who notes trying to remove the tattoo the regular way — with a laser — can make the situation worse.
"It's a very tricky situation. Your tattoo just swells up and becomes wet and itchy and bumpy," he says.
A confusing element of contact allergic dermatitis is that it can develop over time; you can be fine with something for a long time, and then you are not. For some people, the 10th exposure may be the one that triggers the first allergic reaction. Or it could be the 100th or 1,000th. It doesn't make any difference. Once you become allergic to something like hair dye or the lavender in your skin cream, that's it.
"Allergic is all or nothing. Once allergic, always allergic," Skotnicki says.
Confirming the cause of a contact allergic dermatitis problem is done using a patch test, where tiny amounts of suspected allergens are taped to a person's back, sometimes for as long as three days, Sapijaszko says. A red welt will appear if the dermatologist has figured out the correct cause.
Some discoveries mean people must make small changes in their lives.
A body wash or shampoo that contains methylisothiazolinone — an omnipresent chemical that is causing "an epidemic" of allergic dermatitis these days, Skotnicki says — can be replaced with something that doesn't trigger a reaction. A hair colourist who becomes allergic to permanent dye can apply the product wearing a heavy-grade glove. (There's no work-around if your head has become allergic to dye; then it's time to embrace the grey.)
But sometimes bigger changes have to be made. People working in a profession where they cannot avoid exposure to a substance that induces contact allergic dermatitis may need to find a new job.
"If you're a baker and you're allergic to flour, it's pretty hard to work," says Sapijaszko, using a real-life example.