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How Toxic Chemicals Harm Us

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HealthWiki > A Community Guide to Environmental Health > Chapter 16: Harm from Toxic Chemicals > How Toxic Chemicals Harm Us


A woman holds a baby next to a man holding the hands of a boy and girl.
Every member of this family is affected by the chemical factory in their town — some more, some less.

Whether or not a person will be harmed by toxic chemicals, and the kind of health problem that may be caused, depends on many things:

  • what kinds of chemicals and the amounts he or she is exposed to
  • how long the exposure lasts
  • his or her age, body weight, height, and sex
  • his or her general state of health at the time of the exposure


The danger from toxic chemicals is strongest at times when our bodies are growing or changing rapidly:

  • when a baby is forming in the womb
  • when a child is young and growing quickly
  • when a teenager’s (adolescent’s) body is going through rapid changes
  • when an older person’s body slows down and is less able to filter poisons

The effects of toxic chemicals on a person may be severe, such as serious birth defects or cancer. Other effects may be harder to see, such as difficulty learning, slow growth, allergies, difficulty having children, and more frequent illness.

It is often difficult to know whether a certain health problem was caused or was made worse by toxic chemicals. Although toxic chemicals have been proven to cause many different illnesses, because we are exposed to so many chemicals at so many different times, proving that one particular exposure was responsible for an illness is difficult. But many illnesses are more common in places where people are regularly exposed to toxic chemicals.

Even very small amounts cause harm

Traditionally, doctors and scientists follow the rule, “the dose makes the poison.” This means that more of a substance has a stronger effect, and less of it has a weaker effect. For example, poisons such as arsenic or cyanide are only toxic if a person eats too much of them. Even most medicines, like aspirin, are helpful when taken in small amounts, but can be harmful in large amounts.

But even very small amounts of some toxic chemicals can be very harmful. Some chemicals, such as POPs and PCBs, are not safe in any amount.


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