How would you no if you have poison ivy in your mouth?

If you get poison ivy on your tongue, which you can do if you put the leaves in your mouth or are exposed to the smoke from burning poison ivy, you should see a doctor.

There's no topical treatment except perhaps sucking on ice chips to numb the area. Your doctor might consider a course of prednisone.

The swelling might begin to interfere with your breathing. Then you should get to a hospital for treatment to ensure you don't suffocate while getting over this allergic reaction.