Carbon monoxide, commonly referred to as CO, is one of the most dangerous household gases precisely because it cannot be detected by human senses. It has no smell, no color, and no taste, yet it has the ability to kill within minutes under the right conditions. Carbon monoxide is produced whenever fuels such as gasoline, natural gas, propane, kerosene, wood, or charcoal are burned. This means it can be released by cars and trucks, small engines, stoves, fireplaces, furnaces, grills, and many other everyday appliances.

Pesticides are designed to kill living organisms, and for that reason they are, by definition, poisons. While their intended purpose is to control pests such as insects, weeds, fungi, or feral animals, pesticides do not have the ability to distinguish perfectly between their targets and everything else in the environment. Because of this, they can harm people, animals, and ecosystems when exposure occurs.

In biochemistry, a poison is defined as any substance—whether natural or synthetic—that can damage living tissue and cause harmful or even fatal effects in the human body. The way a poison enters the body is just as important as the substance itself. A chemical may be dangerous when swallowed, inhaled, absorbed through the skin, or injected directly into the bloodstream. Each route of exposure changes how quickly and severely the body is affected.