Why is my tongue iching?

It could be contact dermatitis: which is simply an allergic reaction from something you ate or drank, or by contact with an irritant, like solvent, soaps, cleaning fluid or rubber gloves etc. even getting a little bit of fumes in your mouth can cause the reaction: it becomes red, sore or inflamed by contact with the substance.

There are many things that could cause that type of allergic reaction. The best way to figure it out is by visiting your doctor and getting an allergy test.