Next, we’ve got the manual. It basically tells you to not wear it 24×7 for weeks on end so that Fitbit can cover their collective legal rears in the event you breakout with a skin rash.
Note however that it remains unclear as to what percentage of Fitbit Charge/Charge HR/Surge users are still seeing rashes (either due to reaction, or just general irritation of wearing something 24×7). There’s a spreadsheet here by a 3rd party (not me) that collects those concerns. However, do keep in mind that at the volumes Fitbit is shipping these units in (hundreds of thousands) – this is well less than 1% of users (not to minimize that, but to put numbers in perspective). Of course, that doesn’t help if you happen to be in the 1%.