Users are posting complaints on the Fitbit forum, engadget.com, the Consumerist, and other sites, complaining of a red rash.
On Engadget.com, dozens of people have posted comments about getting a skin rash after wearing the device for a few weeks.
Some called their irritation "terrible," or said they had "blisters on their wrist," or said "it looks like a burn," reporting 'blisters on their wrist,' or saying it 'looks like a burn.'
And a picture was posted on twitter by Doug MacLeod showing his skin rash.. He says from the device.
The complaints have similarities - a user has no trouble for the first few weeks of use, but suddenly, they notice redness under the main part of the device - where the sensors, battery, display, and charging port are located.
Several users who consulted doctors were told it had all the hallmarks of an allergy to the nickel in the stainless steel on the band.
The maker of Fitbit also says it could be nickel allergies, or bacteria getting under the band.
Fitbit Force came out last fall, and retails for $130.
Last fall, Action News reported on fitness bands, and tried out the Fitbit Flex. So far, we have not heard any similar complaints about the Flex or the other trackers we tried.