When the body is exposed to a hazardous chemical, its internal defenses try to remove the unwanted substances. The primary internal defense is excretion of the contaminant with other wastes in the feces or urine. Prior to excretion, primarily the liver and kidneys filter wastes. As a result, these two organs are both subject to damage from toxic substances, storing in their tissues what they are unable to break down. Portions of the lungs contain cilia, which try to remove particles so that they can be coughed out. Particles that are too small or cannot be removed for other reasons will remain as deposits in the lower part of the lungs (alveoli), where they can cause scaring, fibrosis, or cancer.

Other body defenses against toxic substances are breathing and sweating. When an intoxicated person has the smell of alcohol on his or her breath, the smell indicates that the body is exhaling material it has no use for. Tears also remove contaminants that enter the eyes. However, these defenses contribute only a small amount to the body’s detoxification (that is, its attempt to rid itself of toxic substances).

The body’s ability to defend itself against toxic substances varies with the individual. Small children are liable to be more affected by the same amount of a substance than are larger or older persons. Elderly individuals also may have less ability to remove toxicants from the body. Gender can be a factor in toxic responses; for example, some cancers are sex-linked (such as prostate and ovarian cancers). Personal hygiene and the overall health of an individual can also adversely affect the body’s ability to process certain toxic substances. For example, a smoker is likely to be much more susceptible to lung cancer if he or she has also been exposed to high levels of radon gas.

Exposure to a poison becomes a problem when the material is of a type that inner defenses cannot break down and remove, or when there is more of it than the body can handle. In these instances, antidotes are available for a limited number of substances. However, only about 20 antidotes are in existence for the thousands of poisons in the world—and each antidote may work for only a few poisons.

Clearly, the safest barrier to toxic exposure is the prevention of exposure. This is why it is so important for citizens to be aware of the threat posed by hazardous materials in their own home and community, and to learn to minimize or eliminate unnecessary exposure.