Can You Microwave Styrofoam?
Most styrofoam should not be microwaved. Traditional styrofoam can melt, warp, and potentially release harmful chemicals when heated. However, some food containers are made from microwave-safe polystyrene and will be labeled as such. Always check for a microwave-safe symbol before heating.
Key Takeaways
- Styrofoam is a brand name for expanded polystyrene foam.
- Even microwave-safe containers should not be used if they are cracked, old, or damaged.
- Styrofoam cups for hot beverages are not the same as microwave-safe containers - do not microwave them.
Explanation
Styrofoam is a brand name for expanded polystyrene foam. When heated, it can melt or deform, and there are concerns about styrene and other chemicals leaching into food, especially fatty or oily foods which absorb these compounds more readily.
Microwave-safe polystyrene containers do exist and are specifically designed to withstand microwave temperatures without melting or leaching. Look for a microwave-safe label, often shown as wavy lines, or the words 'microwave safe' on the bottom.
When in doubt, transfer food to a glass, ceramic, or microwave-safe plastic container before heating. This takes just a moment and eliminates any risk of container damage or chemical exposure.
Styrene, the chemical of concern, is classified as a possible human carcinogen by the International Agency for Research on Cancer (IARC). Studies have shown that styrene migration into food increases dramatically at temperatures above 175 degrees Fahrenheit, and microwave heating can create localized hot spots that far exceed this threshold even when the food's average temperature is lower. Fatty and acidic foods are the worst offenders: tomato-based sauces, oily takeout, and cheese-heavy dishes absorb up to 5 times more styrene than dry or starchy foods at the same temperature.
To identify whether a polystyrene container is microwave-safe, flip it over and look for the recycling number inside the triangle symbol. Standard expanded polystyrene foam is marked with a #6 and should never be microwaved. Microwave-safe polystyrene containers are also marked #6 but will have an additional microwave-safe symbol (three wavy lines) or explicit text. If the container has no markings at all, treat it as unsafe. Containers from fast food chains, delis, and takeout restaurants are almost universally not microwave-safe, regardless of how thick or sturdy they feel.
Things to Know
- Even microwave-safe containers should not be used if they are cracked, old, or damaged.
- Styrofoam cups for hot beverages are not the same as microwave-safe containers - do not microwave them.
- One-time-use containers from restaurants are rarely microwave-safe even if made from sturdy-seeming materials.
- Microwaving styrofoam for just 30 seconds at high power can cause visible warping, while 2 minutes or more can cause it to partially melt and fuse to food, making the food unsafe to eat regardless of chemical concerns.