Expanded polystyrene foam (EPS) cups are common in the food service industry, widely used for serving coffee and other hot beverages due to their low cost and excellent thermal insulation. This material, often referred to by the trademarked name Styrofoam, is highly effective at keeping drinks hot for extended periods. However, the convenience of these single-use containers has raised questions among consumers about their safety when exposed to the high temperatures of freshly brewed drinks. Understanding the chemical composition of the cups and how they interact with hot liquids addresses potential health concerns.
The Core Material: What Polystyrene Is
The material used to make these disposable cups is expanded polystyrene (EPS), a synthetic polymer composed of long chains of styrene monomers. Polystyrene is produced through polymerization, where individual styrene molecules link together. This solid plastic is then processed into a foam by incorporating a blowing agent, typically pentane, to expand the beads significantly.
The resulting foam structure is approximately 98% air trapped within tiny, closed-cell plastic beads, making it lightweight. This air-filled cellular structure gives EPS its low thermal conductivity, making it an effective insulator for both hot and cold items. While the material provides superior insulation, its physical properties can begin to change when exposed to temperatures exceeding 167°F (75°C).
The Safety Question: Leaching and Heat
The primary concern regarding EPS cups and hot drinks is chemical migration, known as leaching, which is triggered by heat. When a hot beverage is poured into an EPS cup, the elevated temperature can cause the polymer chains of the cup material to destabilize. This destabilization allows residual styrene monomers and other trace chemicals to migrate from the plastic matrix into the liquid.
Scientific studies show that styrene migration is strongly dependent on the liquid’s temperature and the length of time the beverage remains in the cup. The higher the temperature, the greater the amount of chemical leaching. Furthermore, the chemical nature of the beverage can influence the rate of migration.
Drinks that contain fat, such as hot milk, or acidic substances, like tea with lemon, increase the rate at which styrene leaches from the plastic. The presence of sugar or caffeine in hot drinks can also elevate the amount of styrene released. Typical serving temperatures for hot drinks like coffee or tea (160 to 185°F) fall within the range where leaching is considerable.
Health Implications of Styrene Exposure
Ingesting leached styrene monomers, even in trace amounts, introduces the chemical into the body, leading to scrutiny from health and regulatory organizations. The International Agency for Research on Cancer (IARC) classified styrene as “probably carcinogenic to humans” (Group 2A). This classification means there is strong evidence that the chemical can cause cancer in animals and limited evidence that it can cause cancer in humans.
The U.S. National Toxicology Program (NTP) also lists styrene as “reasonably anticipated to be a human carcinogen.” The primary concern for consumers is not acute, single-use exposure, but the potential effects of chronic, long-term exposure to small, accumulating doses.
Beyond cancer concerns, long-term exposure to styrene has been linked to non-cancerous effects, particularly on the nervous system. Symptoms reported in occupational settings with higher exposure levels include chronic headaches, fatigue, weakness, and depression. While the amount of styrene leaching from a single cup is minute, the regulatory classifications reflect the need for caution regarding repeated exposure.
Safer Alternatives for Hot Beverages
Consumers seeking to reduce exposure to leached chemicals have several options for hot drinks. Reusable containers offer the greatest safety and environmental benefits. Ceramic mugs, glass cups, and stainless steel tumblers are chemically inert and will not leach substances into the beverage, regardless of temperature.
For disposable, on-the-go needs, certified food-grade paper cups are a safer alternative to EPS. Many of these paper cups are lined with plant-based materials like polylactic acid (PLA), which is derived from corn starch and is compostable in industrial facilities. Other options include cups made from natural fibers, such as bamboo or sugarcane bagasse. These alternatives provide functionality without the chemical concerns associated with expanded polystyrene.