The chemistry of 3D printing resin isn't all that different from the curing composites used for restorative fillings. It is a photosensitive polymer that cures into plastic. In its liquid form, 3D printing resin is non toxic if ingested (though please don't). Though non-toxic, liquid 3D printing resin is classified a sensitizer. This means that if you are exposed to it for long enough, you may develop mild allergic reactions to it.
Sensitization can be prevented by always wearing gloves and working in a well-ventilated environment.
In its hardened form, 3D printing resin is akin to plastic, and is non-toxic.
For more information on resin toxicity and classification, consult each resin's safety data sheet (SDS). SDS for SprintRay resins can be found on our website, and SDS for all supported 3rd party resins can be found on the manufacturer's website.