Routes of Entry
Local vs Systemic
The Dose Makes the Poison
A substance can produce the harmful effect associated with its toxic properties only if it reaches a susceptible biological system within your body in a sufficient concentration (a high enough dose). The toxic effect of a substance increases as the exposure (or dose) to the susceptible biological system increases. For all chemicals there is a dose response curve, or a range of doses that result in a graded effect between the extremes of no effect and 100% response (toxic effect). All chemical substances will exhibit a toxic effect given a large enough dose. If the dose is low enough even a highly toxic substance will cease to cause a harmful effect. The toxic potency of a chemical is thus ultimately defined by the dose (the amount) of the chemical that will produce a specific response in a specific biological system.
"All substances are poisons; there is none which is not a poison. The right dose differentiates a poison ." Paracelsus (1493-1541)