Health risks of exposed contact to a capacitive sensor
Yes, there may be a risk for long term wear.  If your electrodes have an ohmic contact with the patient, and they have a DC bias, and they are made of a reactive metal like copper, then you may be generating metal ions on the patient's skin.  Metal ions may cause a chemical burn.

I have an 8 year old scar to illustrate this.  For a few days, I was experimenting with an EKG circuit and I used makeshift copper electrodes.  The burns (two more: on another arm and on a foot) took a month to heal.