Years of cigarette use leave smoke particles and odor molecules that settle into drywall, carpet padding, upholstery, HVAC ducts and wood framing. Source removal such as replacing heavily stained surfaces comes before any fogging treatment.
A heated deodorizing solution is released as a fine fog that travels into the same porous materials the odor reached, then binds with and neutralizes odor molecules. The space must be empty of people and pets during treatment and ventilated afterward. Persistent cigarette odors often need multiple sessions to improve.