Hi,

Nylon is very applicable to wear on the skin - it's the additives such as colorants that may cause irritation.
I would avoid any polymers with butadiene and styrene components. They are not endemic to the human body and may depolymerize and leech out of the plastic.
PLA on the other hand has a lactic acid monomer which is present in the human body. It is biodegradable and entirely safe for contact with the human body.
Also acrylics, silicone, and polyurethanes can be safe for longstanding periods of skin contact.