chemistry

PFAS

PFAS is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand PFAS rather than just read about it. In short: Per- and polyfluoroalkyl substances (PFAS or PFASs) are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. Because of their high chemical and thermal stability, these compounds have long environmental lifetimes, and thus are commonly referred to as "forever chemicals".

Key takeaways

PFAS belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PFAS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PFAS from memory before moving on to harder problems.

Reference excerpt

Per- and polyfluoroalkyl substances (PFAS or PFASs) are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. Because of their high chemical and thermal stability, these compounds have long environmental lifetimes, and thus are commonly referred to as "forever chemicals". The first PFAS, polychlorotrifluoroethylene, was synthesized in 1934. Widespread use of PFAS began in 1938 with the invention of Teflon (polytetrafluoroethylene), a fluoropolymer coating that resists heat, oil, stains, grease, and water. Since their inception, thousands of PFAS compounds have been created. They are used in a wide variety of products including waterproof fabric, yoga pants, carpets, shampoo, mobile phone screens, wall paint, furniture, adhesives, food packaging, firefighting foam, electrical insulation, and cosmetics. PFAS are often found in groundwater, wastewater and soil; wastewater treatment facilities and landfills have the highest levels of pollution. Furthermore, crop uptake of PFAS and bioaccumulation of PFAS into fish, livestock, and wildlife can act as potential routes of human exposure. In addition, areas near airports and air force bases are contaminated from the use of PFAS-containing firefighting foam. Exposure to PFAS, some of which are carcinogens or endocrine disruptors, has been linked to diseases and health conditions including cancers, ulcerative colitis, thyroid disease, suboptimal antibody response or decreased immunity, decreased fertility, hypertensive disorders in pregnancy, fetal and child developmental issues, obesity, and high cholesterol. Due to the health and environmental concerns associated with many PFAS, PFOS and PFOA were listed in the Stockholm Convention on Persistent Organic Pollutants in 2009 and 2019, respectively. However, it is challenging to assess the potential risks of all PFAS due to the large data-gaps in toxicity and physicochemical properties. With thousands of compounds used in various application, only a few have undergone comprehensive biological testing. In some jurisdictions, such as the European Union, further reductions and phase-outs of PFAS are planned. Several companies are voluntarily ending or planning to end the sale of PFAS and PFAS-containing products due to health and litigation concerns. However, major producers and users such as the United States, Israel, and Malaysia have not ratified the agreement and the chemical industry has lobbied governments to reduce regulations.

Definition

Per- and polyfluoroalkyl substances are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. Different organizations use different definitions for PFAS, leading to estimates of between 8,000 and 7 million chemicals within the group. The EPA toxicity database, DSSTox, lists 14,735 unique PFAS chemical compounds. 7 million are listed in PubChem. An early definition stated that PFAS were "aliphatic substances that contain 1 or more C atoms on which all the H substituents (present in the nonfluorinated analogues from which they are notionally derived) have been replaced by F atoms, in such a manner that they contain the perfluoroalkyl moiety, −CnF2n+1". Beginning in 2021, the OECD expanded its terminology, stating that "PFAS are defined as fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached to it), i.e., with a few noted exceptions, any chemical with at least a perfluorinated methyl group (−CF3) or a perfluorinated methylene group (−CF2−) is a PFAS." The United States Environmental Protection Agency (EPA) defines PFAS more narrowly in the Drinking Water Contaminant Candidate List 5 as substances that contain "at least one of the following three structures: R−CF2−CF(R')R", where both the −CF2− and −CF− moieties are saturated carbons, and none of the R groups can be hydrogen; R−CF2−O−CF2−(R'), where both the −CF2− moieties are saturated carbons, and none of the R groups can be hydrogen; or CF3−C−(CF3)RR', where all the carbons are saturated, and none of the R groups can be hydrogen. A summary table of some PFAS definitions is provided in Hammel et al (2022).

Sample chemicals

Common PFAS include:

Perfluoroalkyl carboxylic acids (PFCAs), such as trifluoroacetic acid (TFA) Perfluorosulfonic acids (PFSAs), such as perfluorooctanesulfonic acid (PFOS) Precursors to PFCAs, such as fluorotelomers, including as fluorotelomer alcohols (FTOHs) Precursors to PFSAs, such as perfluorobutane sulfonamide (H-FBSA), perfluorooctanesulfonamide (PFOSA), perfluorobutanesulfonyl fluoride (PFOSB) or perfluorooctanesulfonyl fluoride (PFOSF) Fluoropolymers such as polytetrafluoroethylene (PTFE, aka Teflon)

Uses

Products PFAS are used to produce fluoropolymers by emulsion polymerization. Because they resist heat, oil, stains, grease, and water, they are ingredients in stain repellents, polishes, paints, and coatings. They came into use with the invention of Teflon in 1938. They have been used in products including waterproof fabric such as nylon, yoga pants, carpets, shampoo, feminine hygiene products, mobile phone screens, wall paint, furniture, adhesives, food packaging, firefighting foam, the insulation of electrical wires, dental floss and sunscreen. PFAS have been used by the cosmetic industry in cosmetics and personal care products, including lipstick, eye liner, mascara, foundation, concealer, lip balm, blush, and nail polish. Pesticides including fluazinam and flufenacet break down to produce trifluoroacetic acid. In 2025, a report by the US FDA stated that in 2021, up to 1.4% of cosmetics sold in Europe contained PFAS and as of 2025, less than 1% of cosmetics sold in the US contained PFAS.

Fluorosurfactants

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with PFAS

Start with the simplest possible case. Write down what PFAS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to PFAS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about PFAS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of PFAS

In research: PFAS appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses PFAS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: PFAS is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical hazards, Environment and health, Organofluorides, so understanding it makes those chapters shorter.
In everyday life: Look for PFAS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study PFAS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PFAS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain PFAS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PFAS in simple terms?

Why does PFAS matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study PFAS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on PFAS.