The Fitbit Force is designed to be worn on the wrist at all times. Throughout the day, the activity tracker logs users' movements; at night it keeps track of their sleep. But some users are also reporting an unwanted side-effect of the device's close contact: rashes and skin irritation.

The Consumerist recounts the experience of one Fitbit Force user, Kevin Sanders, who recorded the effect his device was having on his arm in pictures. Sanders started wearing his tracker in mid-November, but noticed a rash developing in late December. After seeking medical advice, the irritation was diagnosed as contact dermatitis.

Fitbit has offered to refund or replace Force trackers for affected customers

Other users have reported suffered similar skin issues. ABC News has published a picture taken by Fitbit Force user Katy Crossen that shows her red, swollen wrist. Crossen described her rash — reportedly developed soon after she started wearing the device — as "initially very bumpy, blistery and scaly." The Sydney Morning Herald shows another picture of a skin complaint reportedly caused by the Force, taken by one Steven Adams.

Fitbit has reacted quickly to the complaints, offering any customers that "feel that they have an allergy related to their Fitbit device" a refund, or a replacement device from any of its tracker ranges. Fitbit says it will handle all shipping costs and provide a refund for any difference in price.