A letter to customers from Fitbit CEO James Park said about 1.7 percent of Force users have reported skin irritation.
"We care about every one of our customers. On behalf of the entire Fitbit team, I want to apologize to anyone affected," he wrote. "From the beginning, we have taken this matter very seriously. We hired independent labs and medical experts to conduct a thorough investigation."
"All Force materials are commonly used in consumer products. However, some users may be reacting to the nickel present in the surgical grade stainless steel used in the device. Other users are likely experiencing an allergic reaction to the materials used in the strap or the adhesives used to assemble the product," the letter said.
"Rest assured we're working on our next-generation tracker and will announce news about it soon," Park said.