Several years ago I started smelling cigarette smoke. Of course, when it happened at Starbucks, I assumed one of the baristas was sneaking a smoke in the back room. (I don't know about the rest of the U.S. but smoking is not allowed in any restaurants or coffee shops in California-thankfully) But then I would notice it in my own house. It wasn't constant and maybe a month would go by and I wouldn't smell it at all. A year ago I found out I had a meningioma close to my optic nerve and had to have it removed surgically. The meningioma had been growing, unbeknownst to me, for 5 years. After my craniotomy, I was told to let the doctor know if I smelled anything odd that no one else could smell. I was told that could be a sign of a brain seizure. Well, truth be told, I have had that cigarette smell maybe 4 or 5 times since my surgery 6 months ago. But I didn't mention it to my doctor as I figured I have had it over the course of 5 years anyway , way before my surgery, and was afraid the doctor may be too eager to put me back on anti-seizure meds which I took for a month after my surgery. Just as an aside, finding the meningioma was unexpected, incidental to another scan I was having. Three doctors told me many people have them and are unaware if they are not causing symptoms. I've often wondered if smelling cigarette smoke was the first sign of the meningioma. A totally unscientific theory.