<s>[INST] Hi, my dad has been having a constant bad odor when he breathes in with no other nasal symptoms (ie. runny nose, mucus, etc.). He becomes nauseous and has headaches due to the constant bad smell. He's been seeing different doctors but no answers yet. He's had a CT scan, and is to the point of getting an MRI. I just wanted an idea of what may possibly going on. [/INST] Hello, Welcome Thanks for consulting HCM,   I have gone through your query,  as you have mentioned that you have bad odor breathing , it can be due to mucus also , dont worry you go to dentist and go for scaling and root planning   Do warm saline gargle two - three times a day.  Brush twice daily and use chlorhexidine mouthwash twice daily. Hope this will help you.  Wishing you good health. </s>