Toxins in Everyday Life - Why Are Toxins Toxic?

A toxin is a substance—bacterial, viral, chemical, metal, fibrous, or radioactive—that poisons or harms a living organism. A toxin may cause immediate, acute symptoms such as gastroenteritis, or cause harm after long-term exposure such as living in a lead-or radon-contaminated home for many years. Some toxins can have both immediate and long-term effects: Living in an environment with cigarette smoke may trigger an acute asthma attack or, after many years' exposure, it may contribute to lung cancer. Although the effects of a toxin may not show up for years, these effects may, nevertheless, be serious. Toxins are often grouped according to their effect on living creatures. They may be called carcinogens, mutagens, and teratogens:

• A carcinogen is any substance that causes cancerous growth.
• A mutagen is an agent capable of producing genetic change.
• A teratogen is a substance that produces malformations or defective development.

The risks posed by environmental contamination may not be blatantly obvious. For example, people or animals with impaired immune systems and who are exposed to these contaminants may take longer (or even be unable) to recover from infectious diseases. Tracking this problem to environmental pollutants, however, can be difficult.