Expanded polystyrene foam, commonly known by the trademarked name Styrofoam, is widely used in modern food service due to its excellent insulation and lightweight nature. This foam, often found in takeaway containers and disposable cups, is a type of plastic that has raised concerns among consumers and health experts regarding the potential for chemical exposure. These worries stem from the foam’s core chemical composition and the conditions under which it interacts with food and beverages. The concern is the migration of trace chemical residues from the plastic into the contents people consume.
The Core Chemical Component: Styrene
The foam used in food packaging is expanded polystyrene (EPS), a polymer created from the chemical called styrene. Styrene is a liquid organic compound that is chemically linked together in a process called polymerization to form the long, stable chains of polystyrene plastic. The resulting polymer is largely inert, but safety concerns arise from the manufacturing process.
Not all of the styrene monomer is successfully converted into the polymer during production, leaving trace amounts of the unreacted monomer residual within the final foam product. This residual styrene content can be significant, sometimes measured in the tens to hundreds of milligrams per kilogram of material. This residual chemical component is the primary contaminant that has the potential to migrate out of the food-contact material.
Exposure Pathways: When Does Leaching Occur?
Leaching from polystyrene into food is heavily influenced by several factors related to the food or drink it contains. High temperatures significantly accelerate this process, which is why pouring hot coffee into a foam cup or microwaving food in a polystyrene container heightens the risk of exposure. The heat increases the kinetic energy of the styrene molecules, making it easier for them to break free from the polymer structure and enter the food matrix.
Contact with foods that are high in fat or oil also markedly increases chemical migration. Styrene is a lipophilic (fat-soluble) compound, meaning it dissolves readily into fatty substances. Therefore, a container holding oily foods, such as fried rice, french fries, or ice cream, will draw out more styrene than one holding plain water. Studies have shown that both high temperatures and high fat content increase the level of styrene migration from polystyrene.
Acidic foods and beverages, such as citrus juices or tomato-based sauces, can also promote the breakdown of the polymer and facilitate the release of styrene. While temperature and fat content are the most frequently cited factors, the corrosive nature of acidic contents can similarly compromise the integrity of the foam. The combination of these conditions—such as a hot, fatty, and slightly acidic soup—creates the most favorable environment for the maximum transfer of residual chemicals into the meal.
Regulatory Status and Documented Health Effects
Styrene has been classified by authoritative health organizations. The International Agency for Research on Cancer (IARC), an arm of the World Health Organization, classifies styrene as a Group 2B agent, meaning it is “possibly carcinogenic to humans.” This classification is based on limited evidence in human studies and sufficient evidence from animal studies demonstrating carcinogenicity.
The US National Toxicology Program (NTP) lists styrene as “reasonably anticipated to be a human carcinogen.” These classifications are not definitive proof of cancer risk from low-level dietary exposure, but they signal a potential hazard that warrants caution and regulation. The styrene metabolite, styrene-7,8-oxide, is classified by IARC as a Group 2A agent, or “probably carcinogenic to humans.”
Beyond cancer concerns, chronic exposure to styrene, particularly in occupational settings, has been linked to non-cancerous health effects on the nervous system. These documented effects include symptoms like headaches, fatigue, weakness, and depression. Low-level, long-term exposure may also be associated with minor effects on kidney function and neurotoxicity. While the Environmental Protection Agency (EPA) has not yet issued a formal carcinogen classification, it has identified styrene for risk evaluation under the Toxic Substances Control Act (TSCA) program to determine if it presents an unreasonable risk to health.
Practical Steps for Minimizing Risk
The most important step is to never heat food or beverages in a polystyrene container, especially avoiding microwaving. High heat dramatically increases the rate of chemical leaching. The high heat exacerbates the migration of residual styrene into the food or drink.
When receiving hot or oily takeaway food in a foam container, transfer the contents immediately to a safer container, such as one made of glass or ceramic, before consumption. This action minimizes the contact time between the food and the plastic. It is also prudent to avoid storing acidic foods like marinated meats or coleslaw in polystyrene for extended periods.
Consumers can choose safer alternatives for food service and home use to eliminate the exposure risk entirely. Secure choices include:
- Reusable containers made from glass or stainless steel.
- Certain plastics labeled as microwave-safe and BPA-free.
- Biodegradable containers made from molded paper pulp.
- Disposable containers made from cornstarch.