Actually, after one trip to Las Vegas several years ago, I went to see an allergist. It was about a year after I quit smoking. He explained to me that smokers may be allergic to their own smoke but that when they smoke they are doing the same thing as having "allergy shots" and exposing themselves to the allergen thereby giving themselves immunity. When they quit and the exposure stops, the allergy returns. Same symptoms as ragweed or other pollens. Red running eyes, nasal passages clogged and breathing impaired.