Perfluoroalkyl and polyfluoroalkyl substances ( PFAS ) are synthetic organofluorine chemical compounds which have multiple fluorine atoms attached to an alkyl chain. They have been commercially produced in vast quantities since the 1940s, and have applications in the manufacture of lubricants, water repellents, fire retardants etc etc.

They are extremely persistent in the environment. Permanent traces can now be found in a wide range of living organisms worldwide. There are now almost 10,000 different PFAS chemicals in use.

It's known that even in minute quantities PFAS can have severe adverse effects on the human immune response. For example, by reducing the effectiveness of vaccines - in some cases by up to 40% (for details see the report referenced below).

They're also implicated in increased incidences of colitis, various cancers, and other diseases.

The full extent of the problem, and its biological mechanisms are currently unknown.

Further reading PNAS April 13, 2021 118 (15)