There are two main effects of indoor air pollution. The first is the effect on the home itself: everything gets dirty, especially if the pollution is particulate matter (e.g. soot), and structural problems can arise from things like mold and mildew. The second is the effect on your health if you live in the home. Let's look at what can happen.
In the short term
Toxicologists call these effects "acute" because they happen immediately, or almost immediately. The effects themselves can be annoying and temporary, such as a slight cough or headache, or more serious and permanent, such as sickness and death.
The most obvious and well-known example of such an effect is from carbon monoxide. This gas is released by burning almost anything, though appliances using natural gas can be particularly bad. Carbon monoxide is poisonous and should always be vented outside. If it accumulates inside a building, the inhabitants will suffer from headaches, dizziness, nausea, fatigue, weakness, confusion, disorientation, and eventually death.
The problem here is that, like many air pollutants, carbon monoxide poisoning symptoms are very similar to other afflictions – in this case, food poisoning or the flu. It may take some time before the real culprit can be tracked down and corrected, especially if the leak is tiny and the effects occasional. In the case of carbon monoxide, detectors are recommended in any home using one or more combustion appliances, helping solve the problem of diagnosis.
In the long term
Toxicologists call these effects "chronic" because they happen over an extended period of time, usually manifesting years after they began. The effects can be minor but usually worsen over time, eventually causing severely debilitating conditions.
Two good examples of chronic effects come from radon and formaldehyde. We've mentioned the latter elsewhere on the site because it is present in many construction materials. Over time, the formaldehyde seeps out of these materials into the home, slowly poisoning the inhabitants. The chemical is also present in old fiberglass insulation, combustion sources (particularly kerosene heaters and unvented gas stoves), shampoos, plastics, paints, and a variety of other goods. It's almost impossible to avoid formaldehyde in one form or another.
Formaldehyde causes difficulty breathing, nausea, and makes your eyes and throat water and burn. Some people are sensitive to as little as 3 parts in every 100 million, and sensitivity can be worsened by continued exposure. Formaldehyde can trigger asthma attacks and, over greatly extended periods, cause cancer.
Radon is a natural radioactive gas. It is colorless, odorless, and seeps into the home from the surrounding earth, invading through cracks in basements and foundations. It is particularly dangerous in passive solar homes because they are more airtight than traditional constructions, which means they retain radon better.
Now, let's not mistake the danger here: small amounts of radioactivity in the air are not, in themselves, perilous to your health. The problem is that, unlike most radioactive materials which remain fairly similar when they decay, radon turns into radioactive lead. You read that correctly: a gas which, when it decays, turns into a