We were quite impressed with Jawbone Up24 when we reviewed it. But, a few weeks later, things soured a bit when an editor developed a rather unpleasant rash from the device. Turns out it's not all that uncommon a reaction. While the usual list of concerns for gadget buyers focuses on specs, features and in certain cases portability, with the advent of the wearable, consumers need to start worrying about their own skin sensitivity as well. Are you particularly susceptible to bacterial infections? Are you allergic to nickel or latex? Then that's something that you'll have to take into consideration when it comes time to pick out a fitness tracker or smartwatch.

In addition to our anecdotal experience, we've heard similar complaints about past versions of the FuelBand and the Engadget forums are alive with reports of sores and rashes associated with the Fitbit Force. While a sensitivity to nickel would be the most immediate suspect in cases like these, according to dermatologist J. Todd Williams, M.D., it appears something else is to blame. The Force does contain trace amounts of the metal in the surgical-grade stainless steel used on its body, but the position of the rashes would seem to rule out it out in many cases. The same would be true of Up users, as only the cap emblazoned with the Jawbone logo contains nickel plating. And since the Up is coated in a hypoallergenic rubber and the Force forgoes latex as well, it seems an allergy to that particular polymer isn't the culprit either.

Instead, it appears that trapped moisture and bacteria are the most likely causes of discomfort. Wrist-worn devices like the Up, Force and Flex tout their ability to shrug off water and many users simply never take them off, even in the shower. As Williams explained, "there is one type of dermatitis called 'irritant' dermatitis that just comes from irritation from water/sweat etc..." Essentially, a build up of moisture (which can also encourage bacterial growth) against the body can cause sores and rashes on those with particularly sensitive skin. People commonly experience similar reactions to watchbands, bracelets and rings. For instance, Williams says, newlyweds often complain of irritation from water being trapped under their rings while washing dishes.

While the solution might be as simple as cleaning your wearable regularly with antibacterial soap and taking it off while you shower, Fitbit is taking the complaints seriously. If customers feel they're experiencing an allergic reaction to their tracker, the company is offering either a refund or a replacement device. And, obviously, it will foot the bill for all shipping costs and refund any difference in price, should you choose to replace your Force with a Zip, for instance. Fitbit insists it tests all its materials thoroughly and meets a variety of international standards for safety, but there's no accounting for the unexpected. Jawbone representatives have told us they're looking into the issue, and we'll update this post if we receive a statement from the company.

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