Several studies suggest that the intelligence quotient (IQ) has been declining since the early 2000s. The hypothesis of Barbara Demeinex is that endocrine disruption is one of the main factors contributing to this decline and in particular, that which affects the thyroid hormone. Many of the chemicals we are exposed to, including thyroid axis disruptors, not only circulate through the mother’s blood but also cross the placental barrier and into the amniotic fluid, at high enough levels to interfere with thyroid signaling. Hence, several epidemiological studies have shown in recent years that children born to mothers exposed to a high rate of thyroid disruptors have a lower IQ than those whose mothers did not incur the same exposures. The implementation of regulation is slow, despite potentially considerable societal, economic and health costs.