Concerns about chemical coatings in the kitchen often lead to the question of whether traditional cast iron cookware contains Per- and polyfluoroalkyl substances (PFAS). Bare cast iron is definitively free of PFAS, making it a safe choice for cooking. The confusion arises because PFAS are widely used in other non-stick products, causing consumers to question all non-stick surfaces, including the naturally developed surface of seasoned cast iron. Understanding the material science of cast iron clarifies why this cookware is exempt from PFAS concerns.
What Exactly Are PFAS?
Per- and polyfluoroalkyl substances (PFAS) are a vast class of manufactured chemicals, numbering over 15,000 different compounds, used globally since the 1940s. These synthetic compounds were designed for high resistance to heat, water, and oil. This chemical stability made them desirable for various industrial and consumer applications, ranging from stain-resistant fabrics to firefighting foams and, notably, non-stick coatings.
PFAS are often called “forever chemicals” because they do not break down easily in the environment or the human body. This persistence is due to the exceptionally strong bond between carbon and fluorine atoms in their molecular structure. Their resistance allows them to accumulate over time, leading to long-term health and ecosystem concerns, including liver damage, kidney issues, and increased risks of certain cancers.
The Composition of Bare Cast Iron
Traditional, bare cast iron cookware is fundamentally an alloy composed primarily of iron and a high percentage of carbon, typically ranging from 1.8% to 4%. Silicon is another standard alloying element, present in concentrations of 1% to 3%, which aids the casting process. This simple metallurgical composition, consisting of metal elements and carbon, confirms that no fluorinated compounds are part of the raw material.
The desirable non-stick surface on bare cast iron is not a synthetic chemical coating but a layer called seasoning. Seasoning is created when cooking oils or fats are applied to the metal and baked at high temperatures. The heat causes the oil to undergo polymerization, where fatty acid molecules bond together and harden into a durable, plastic-like film chemically bonded to the iron surface. This film is completely free of the carbon-fluorine bonds that define PFAS.
Distinguishing Cast Iron from Non-Stick Cookware
The confusion about PFAS in cast iron largely stems from its association with conventional non-stick cookware, which uses a completely different technology. Most traditional non-stick surfaces are made from a fluoropolymer known as Polytetrafluoroethylene (PTFE), which is commonly recognized by brand names like Teflon. PTFE is itself a type of PFAS.
For many years, the manufacturing process of PTFE coatings relied on Perfluorooctanoic acid (PFOA) as a processing aid. PFOA is a well-known “forever chemical” linked to health concerns, leading to its phase-out from production in the U.S. and other regions. While modern PTFE cookware is typically PFOA-free, it still contains PTFE. Some manufacturers have replaced PFOA with other, less-studied PFAS compounds like GenX. Cast iron, with its oil-based seasoning, is entirely separate from this fluorinated chemical technology.
Clarifying Enameled Cast Iron Safety
Enameled cast iron is a popular variation that uses a coating of vitreous enamel, which is essentially a type of glass fused to the cast iron base at extremely high temperatures. This glass-like layer is composed of silica and other minerals. It prevents the underlying iron from rusting and eliminates the need for seasoning.
Since the enamel is a non-reactive, inert layer of fired glass, it does not contain the fluorinated compounds that classify a substance as PFAS. Safety concerns sometimes relate to the potential use of heavy metals, such as lead or cadmium, in the pigments used for coloring the enamel, particularly in older or lower-quality products. Reputable manufacturers adhere to strict testing protocols to ensure their enamel coatings are free from these harmful metals, confirming that high-quality enameled cast iron remains a PFAS-free option.