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Discussion
A typical dose-response curve is shown in Figure 3, which plots the relationship between the toxicant dose and the health effects.
In addition, a chemical can produce harmful effects to one living organism while not harming another (selective toxicology). For example, an antibiotic may kill strep throat bacteria, but it will not kill you.
People can also respond to chemical substances in different ways. Some may be exposed and may not develop a negative effect, while others may be more sensitive to a chemical and can develop negative effects from an exposure.
No two individuals are the same; therefore the response to a dose varies considering age, lifestyle, and genetics (biological variation). Yet, if there is no exposure to a chemical, there will not be an effect.
When an organism is exposed to a toxic substance, it follows toxicity phases.
1st phase: Exposure phase - a toxicant is taken up by the organism's system via the mouth (oral), lungs (inhalation), or skin (dermal).
2nd phase: Processing phase - the toxicant is transported and stored inside the body. The rate at how it is processed varies from person to person.
3rd phase: Expression phase - describes the resulting effects that appear in the organism (e.g. lesion or headache).
Increasing effect no effect range range of increasing effect with increasing dose
Figure 3. A dose-response curve showing as the dose increases, so does the response Source: Dose-response curve - Labster/2025 Toxicology Education Foundation.