Polypropylene is a widely used plastic, recognized for its durability and versatility. It appears in a vast array of everyday items, including food containers, automotive parts, and various medical devices. Its widespread presence leads many to question its safety, particularly regarding any potential link to cancer.
Polypropylene and Carcinogenicity
Pure polypropylene polymer is generally considered chemically stable and largely inert, meaning it does not readily react with other substances. This inherent stability contributes to its broad acceptance. The International Agency for Research on Cancer (IARC) has classified polypropylene in Group 3, “not classifiable as to its carcinogenicity to humans.” This indicates insufficient evidence from human and animal studies to determine if it causes cancer. While one early animal experiment involving subcutaneous implantation of polypropylene discs or powder in rats induced local sarcomas, no epidemiological studies or human case reports were available to the IARC working group at that time. The polymer itself is not considered a direct carcinogen.
Potential Concerns with Additives and Contaminants
While pure polypropylene polymer is highly inert, final plastic products are not made solely from this polymer. Manufacturers incorporate various additives to achieve desired properties such as flexibility, color, UV resistance, and heat stability. These additives can include stabilizers, pigments, antioxidants, and plasticizers.
The primary health consideration with polypropylene products shifts to these added substances. Some additives, especially those used in the past or in non-food-grade applications, could potentially pose risks if they leach out of the plastic and into food or beverages. Strict regulatory standards are in place for plastics intended for food contact and medical use. Notably, polypropylene does not contain bisphenol A (BPA), a chemical found in some other plastics that has raised health concerns.
The Issue of Microplastics
A contemporary concern involves microplastics, tiny plastic fragments less than five millimeters long. Polypropylene products, like other plastics, can shed these particles over time due to wear, degradation, or repeated use. These microplastics can then enter the environment and the human body through ingestion or inhalation.
While studies have identified microplastics in human tissues, there is no conclusive evidence directly linking polypropylene microplastics to the development of cancer in humans. Some laboratory studies, particularly on breast cancer cell lines, have explored how polypropylene microplastics might affect cell behavior, showing changes in gene expression related to metastasis at relatively high concentrations. However, these in vitro findings require further investigation through long-term human exposure studies to draw definitive conclusions about cancer risk.
Safe Handling and Regulatory Oversight
Governmental bodies like the U.S. Food and Drug Administration (FDA) regulate plastics used in contact with food. The FDA approves specific types of plastics, including polypropylene, for food contact applications, meaning they are considered safe for their intended use. This approval process involves rigorous evaluation to ensure the materials do not release harmful substances into food.
Consumers can take steps to use polypropylene products safely. Look for the #5 recycling symbol, which typically identifies polypropylene plastics. When heating food, only use polypropylene containers specifically labeled “microwave-safe” to minimize any potential for material degradation or chemical migration. Avoiding visibly damaged or heavily scratched plastic containers for food can help maintain their integrity.