Can you safely assume you are not allergic to a poison sumac plant if you have come in contact with it and 12 hours later you still have not developed a rash? Why or why not.

I do not think you should assume that you are resistant to poison sumac just because you came in contact with it and did not get a rash. As far as why not I am not sure. Maybe because your genetics have given you the ability to resist the oil when it comes into contact with your skin.