There are several dangerous indoor air pollutants in your home and office but the 4 most dangerous indoor air pollutants are cigarette smoke, formaldehyde, radioactive radon-222 gas, and very small fine and ultra fine particles.
Carbon Monoxide and smoke from cooking and burning food are also harmful to breathe in but not as harmful as the above listed air pollutants.
Indoor air quality is actually worse than outdoor air quality so it's important to get outside as much as possible to get some fresh air even though it's not that fresh.