History of Fire Breathing
Basically, it is using a flammable liquid and igniting the forced stream with an open flame.
In countries with access to multiple fuels, Ultra Refined Lamp Oil is the choice of professionals. In America it evolved from using gasoline, to white gas (Napfa) to lamp oil, then ultra refined lamp oil see also https://en.wikipedia.org/wiki/Kerosene
Due to the hazards, it is strongly recommend that you engage a professional fire performance artist as your teacher
Breathing with Powders
Fine organic powders such as creamer and cornstarch have been used
A drawback of creamer is that it is not sterile and if inhaled to grow bacteria in your lungs
Cornstarch (aka "Dust") is sterile and much more safe to hold in your mouth
Cornstarch is a much lower temperature than Ultra Refined Lamp Oil
Once cornstarch lands on a surface it is no longer flammable, so no third degree burns on the face, or chemical pneumonia. HOWEVER, if you breathe directly on your body, or bring the flames very close to you, you can get burned.
Powder is not good on the lungs, but it could take several times of exposure before you might get "Baker's Lung". Learn to not talk or breathe from your mouth while you breathe cornstarch.
If you try to do it by yourself without professional instruction, there is a good chance that you will end up with an unpleasant plug of mucus-like corn starch in your throat. Also learning to have powder in your mouth takes practice, always have water on hand to clear out your mouth! And with all fire performing, always have a trained fire safety with you.
Due to the skill set needed to properly breathe the powder, I recommend taking classes from a professional cornstarch fire breathing instructor.