Hi Earlytwenties,
Walker Ultra Hold has been around for a long time without any issues. The federal government in the US and major countries around the world regulate and monitor the usage of chemicals. They issue Safety Data Sheets (SDS) to the public. Prior to 2012 these disclosure sheets were known as Material Safety Data Sheets (MSDS) with the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). All manufacturers are required to have a labeling and hazardous communication programs up to date. All manufactures of glues and tapes make this information available to the public if requested. Walker will provide this data sheet to you if you request it.

An independent lab conducted extensive tests on Ultra Hold in 2007 and found that it did not present a health risk. Note that a chemcial can cause an allergy but not be toxic. Even milk causes an allergic reaction in some people. It's always a good idea to test a small piece of skin with glue just to make sure there is no allergic reaction.
Regards,
John