When I hear talking about forever chemicals, they are usually described as “chemicals are not affected by naturally occurring reactions, and that accumulate in the bodies of living beings”. By accumulating, they cause all sorts of health issues.
What I don’t understand is how they cause these health issues. If these chemicals do not participate in regular reactions, how do they cause issues?
I am not claiming that the research in the subject is wrong, I am missing the link between “these things don’t react with anything” and “these things still cause all sorts of health problems”.
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The replies so far are accurate as far as possible mechanisms of toxicity, which is your question. But it helps to zoom out a bit- in order to do an experiment, you need a control group. Give one set of rats a dose of halogenated hydrocarbons, raise a second group of rats without them, compare their disease rates. But [these chemicals are in wild animals everywhere except Antarctica](https://www.theguardian.com/environment/2023/feb/22/animal-toxic-pfas-contamination-study) and even [on top of Mt. Everest.](https://www.theguardian.com/environment/2023/feb/22/animal-toxic-pfas-contamination-study) These chemicals are used in the factories that package food for lab animals, and they’re used in the farming process, so it is exceptionally difficult to raise lab animals without them. Now, one might start with the assumption that rats with *tiny* quantitates of these chemicals are going to show tiny effects, and larger doses will show larger but similar effects. That is how most toxins work. But other chemicals, like dioxin, the main contaminant in Agent Orange, and Bisphenol A, the hormone mimic in plastic, [have strongly non-linear dose- response curves.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2475953/) Tiny doses may have the same response as larger doses, because they have already saturated the sensitive receptors they bind to. *Both of those chemicals are highly persistent in the environment and are sometimes described under the umbrella term “forever chemicals”, although that term is more often applied to precursors of chemicals like Teflon.
It was irresponsible to release these things without fully testing the health consequences, and now they are so widespread that it is difficult to raise a rat with zero exposure as a comparison subject. I think it is most reasonable to be only mildly alarmed, the rate of cancer has mostly increased only mildly since the chemicals have been invented, and most of that increase is due to people getting fatter and living longer. But comparison is difficult- cigarette smoke and coal smoke was everywhere when these things were invented. Before cigarettes and coal were widespread, people died young of infectious disease, and medical diagnosis was wildly inaccurate, so we really have only a foggy idea what the cancer rate was before the year 1900.
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