There are a number of different pollutants you should be aware of. Carbon monoxide is probably the most dangerous of all of them and it's likely the one you’ve heard about the most. It’s an odorless gas that can be caused by a number of different factors such as propane heaters or gas stoves. The CDC reports that 400 people die every single year in the United States from accidental CO poisoning. Radon is another pollutant you should be checking for. The Department of Health and Human Services in the United States states that one in every five homes have high levels of this odorless gas. Other, slightly less harmful pollutants are things like dust from carpets or fabrics, perfumes from occupants in your home, pollen, and bacteria and molds from damp areas in your home or stagnant water that can be irritating for some populations and even be the cause of allergic reactions.