PFHxS

What is PFHxS?

Perfluorohexanesulfonic acid, or PFHxS, is a man-made chemical in the PFAS family — a group of substances often called "forever chemicals" because they break down very slowly in the environment and in the human body. PFHxS belongs to a subgroup called short-chain PFAS, meaning its molecule is slightly smaller than older PFAS compounds like PFOA or PFOS. Like all PFAS, it can build up over time in water, soil, and living things.

Where does it come from?

PFHxS has been used in industrial processes and in many everyday consumer products, including stain-resistant fabrics, water-repellent clothing, food packaging, and some firefighting foams. It has also appeared in certain cleaning products and surface coatings. When these products are made, used, or thrown away, PFHxS can enter the environment and eventually reach drinking water sources.

Health concerns

Research on PFHxS is still limited compared to better-studied PFAS like PFOA and PFOS. Some animal studies have associated PFHxS with effects on the thyroid, liver, and immune system, but strong human evidence is not yet established. Because data is still emerging, the EPA has identified it as a chemical of concern. If you have specific health questions, consult a healthcare provider.

EPA standard

The EPA set a Maximum Contaminant Level, or MCL, of 10 parts per trillion (ppt) for PFHxS in 2024. An MCL is the highest amount of a contaminant allowed in public drinking water. This means water utilities must test for PFHxS and take action if levels exceed that limit.

What you can do

If PFHxS is detected in your water, consider using a certified water filter — reverse osmosis systems and ion exchange filters are most effective at removing PFAS like PFHxS, according to the EPA. Granular activated carbon filters may also help but are generally less effective. Remember, boiling water does not remove PFAS and will not make it safer to drink.