Do acrylic retainers -used after braces are off- release any sort of toxic chemicals?

Skin patch test: Retainers are usually made from a material called methyl methacrylate. One way to test for sensitivity is to get a small disk, use an non-allergic bandaid and place this on your forearm for 48 hours. If there is a redness at the site when you remove the bandaid, then you might have an allergic reaction and there are other substances that an be used.

No: Unless you are allergic to acrylic. Have your family doctor or allergist test you if you have a problem. In 40+ years I have never seen case. What can be a problem is not cleaning the retainers and having a contact infection. Take retainers out and brush gently when you brush your teeth. Also 1x/day in denture cleanser is a good idea.