Hi,
There are actually tons of articles about this, for example in pathology and biomedical engineering.
Keywords: cytotoxicity, biocompatibility, erythematous reactions

What I know is that nylon is much better for skin contact than many other polymers.
What you also want to look for is a polymer with little hydrolytic effects so it retains its original properties over time.
Nylon loses a lot of strength when in contact with moisture and acids for prolonged periods. That also goes for PLA and other biodegradable materials.
ABS is suitable for skin contact, it is also used in the adult industry and tattoo dyes. It is the additives that may cause reactions. Look into the MSDS of your specific filament.
Also PMMA filament is suitable and has been used in prosthetics for years, skin reactions may occur but will be very rare.