The thinking behind using animals to study human reactions is just as flawed: We assess chemicals as if humans were 70-kilogram rats-as if simply scaling up results from animal tests could help us predict a chemical's effects on humans. But we ingest, metabolize, and react to chemicals differently than animals in labs do. One of the standard animal experiments used to evaluate potential skin irritation, for instance, fails to predict effects on humans about half the time.
Animal tests are also time consuming and expensive; a single test on just one chemical can take three years to complete and cost millions of dollars. Because they can be difficult to interpret, animal tests often lead to even more animal tests rather than the implementation of regulations that protect the public and the environment. And there's the obvious cruelty: Animals used in chemical experiments are never given any pain relief, even though scientific evidence clearly shows us that they suffer.
The lack of translation from animal to human stems from several of these testing methods' intrinsic flaws. One is that animal experiments only involve very high doses of one chemical at a time, whereas humans are often exposed to low doses of hundreds of different chemicals and products simultaneously. Second, animal tests don't account for human diversity. Our life stage, diet, health status, and genetic makeup all play a part in how we might respond to chemical exposure, and animal tests don't reflect this diversity.