was a bit taken aback that the doctor answering the following question didn't ask the patient whether he or his partner were smokers and whether they might be smoking in the vicinity of their CPAP machine:

"Q: I sense an odor within my nose; it smells like a dirty ash tray. I use CPAP for sleep apnea. Could this be the cause or could the odor be from a sinus infection?

A: Using CPAP (Continuous Positive Airway Pressure) for sleep apnea can lead to nasal dryness and crusting and sometimes an abnormal odor. The humidifier on the CPAP machine helps, but is not always enough. Performing nasal irrigation to clean out the nose in the morning may alleviate your symptoms.

However, multiple causes of abnormal smell in the nose are possible. The most common causes are nasal or sinus infections."

http://health.msn.com/health-topics/articlepage.aspx?cp-documentid=...