From the desk of Bassel Paul Gebrael DDS, Dip. Perio, FRCD(C), FICD

Type 2 bad breath originates from the respiratory tract all the way from your nose down to your lungs and could be the result of inflammation due to allergy or obstruction and/or a viral or bacterial infection.

This kind of bad breath that originates in the respiratory system accounts to somewhere between 3% to 10% of all cases

There are variations in the anatomy of your nose and sinuses that may predispose you obstruction and infection. 

Young children with constantly inflamed nasal passages are prone to bad breath. 

If your nose is obstructed and you’re breathing through your mouth, it might cause your mouth to dry up and that also causes bad breath.

When your tonsils are swollen due to inflammation, mucus and food debris can build up inside of them and bacterial colonies can break down this accumulated debris and release volatile malodorous substances into your breath.

The bacterial debris inside of your tonsils may also calcify into tonsil stones, and these stones have a strong association with bad smell from the mouth

Gases produced in the respiratory system may also stimulate your sense of smell and give you the sense that you have bad breath, even when it is not noticeable to others.