PFAS stands for per- and poly-fluoroalkyl substances and include (PFOS and PFOA). Known as “forever chemicals”, PFAS are fluorinated compounds in manufactured chemicals used in the production of non-stick pans, fast food packaging, firefighting foams, and more. PFAS are called forever chemicals because their chemistry keeps them from degrading in normal environmental conditions. They can therefore persist in the environment for long periods of time.
Some brands use PFAS for their stain resistant properties. Research states exposure to high levels of PFAS can potentially impact health and the danger of PFAS is greater if ingested. Some brands have been found to use these chemicals in the production of period underwear —in the “moisture wicking” layer—bringing PFA's in direct contact with the vagina.
You can find out more about PFAS here.