Polystyrene foam, widely recognized by the brand name Styrofoam, is a material frequently used for disposable food packaging, hot beverage cups, and insulation. The widespread use of this material, particularly in food service, has led to public discussion and concern about its safety. This concern stems from the chemical components used to manufacture the material and the possibility of human exposure. The primary goal of this article is to provide clarity on the potential cancer risk associated with this common material, based on scientific evidence from regulatory and health organizations.
Defining Polystyrene and Styrene
The foam used for disposable cups and takeout containers is technically Expanded Polystyrene (EPS), which is often mistakenly called Styrofoam. Styrofoam is actually a trademarked brand name for extruded polystyrene foam used primarily for building insulation, not food service products. Polystyrene is a synthetic plastic polymer created by linking together many individual molecules of a chemical compound known as styrene.
Styrene is the monomer building block used to create the plastic, and it is this specific chemical that is the focus of health concerns. The finished Polystyrene polymer is generally considered inert and stable, but some residual, unreacted styrene monomer can remain trapped within the foam structure. Styrene is a colorless, oily liquid used in the production of many different plastics, synthetic rubber, and resins.
Official Carcinogen Classification
The question of whether Polystyrene poses a cancer risk centers on the classification of its monomer, styrene, by major regulatory bodies. The International Agency for Research on Cancer (IARC), a branch of the World Health Organization, has classified styrene as “Group 2A: Probably carcinogenic to humans.” This classification means there is limited evidence of cancer in humans but sufficient evidence of carcinogenicity in experimental animals.
The human evidence is based primarily on studies of workers in the reinforced plastics industry who experienced high-level, occupational exposure, suggesting a possible link to lymphohematopoietic malignancies. The IARC classification also considered that styrene’s major metabolite, styrene-7,8-oxide, is genotoxic and reacts directly with DNA, providing a plausible biological mechanism for harm.
The U.S. National Toxicology Program (NTP) similarly lists styrene as “reasonably anticipated to be a human carcinogen.” This NTP classification is based on limited evidence in humans, sufficient evidence in animals, and supporting mechanistic data showing DNA damage in human cells exposed to the chemical. These classifications apply to the styrene monomer itself, not the finished Polystyrene product, which is generally considered stable. However, the presence of unreacted styrene in the final product provides the route for potential human exposure.
Pathways of Human Exposure
Human exposure to styrene from Polystyrene products occurs through the process of chemical migration, where the residual monomer leaches out of the plastic and into food or beverages. Studies have repeatedly shown that styrene can contaminate food stored in Polystyrene containers, even at normal temperatures. The extent of this leaching is not uniform and is significantly influenced by the temperature and composition of the contents.
Hot liquids, such as coffee or soup, and microwaving the containers dramatically increase the rate at which styrene molecules migrate out of the plastic and into the food. Furthermore, food items with high fat or high acid content can facilitate this chemical transfer. For example, fatty foods like dairy products or acidic foods like tomato-based sauces induce more styrene leaching than water-based contents.
While consumer exposure from food containers is generally at a low level, it is distinct from the high-level, chronic exposure observed in occupational settings that formed the basis for the carcinogen classifications. However, the consistent finding of styrene contamination in food suggests a need for caution regarding consumer exposure scenarios. The presence of microplastic particles from Polystyrene has also been documented to migrate into food simulants, adding another dimension to the exposure concerns.
Practical Guidance and Alternatives
Given the evidence of styrene migration, consumers can take practical steps to minimize their exposure when handling Expanded Polystyrene containers. A primary recommendation is to never heat Polystyrene food or beverage containers in a microwave, as the high temperature significantly increases the release of styrene. It is also advisable to avoid putting very hot, acidic, or fatty foods directly into these foam containers for long periods.
When seeking alternatives, many safer options are now widely available for food service and storage. Reusable glass or ceramic containers are the most effective way to eliminate chemical leaching and are suitable for heating food.
Alternative Materials
For disposable options, materials that do not contain styrene are preferred. These include:
- Sugarcane fiber (bagasse)
- Bamboo
- Paperboard
- Polypropylene (plastic #5)
- Polyethylene terephthalate (PET, plastic #1)
These alternatives are often compostable or recyclable and considered more stable for food contact applications.