Some smells can come from liver or kidney
diseases, (I think it's called ketosis), or from acid reflux in
the stomach, or from a brain injury
8. Some smells can come from having a bad mix of bacteria in the intestines, and somehow the smell comes out through the sinuses or lungs. The best solution that I have seen is The Schwarzbein Principle by Dr. Diana Schwarzbein, MD.
9. There is a disease called atrophic rhinitis, which involves the decay of the mucus membranes in the sinuses.