Short answer:
You should not put most Styrofoam in the microwave unless the container is explicitly labeled “microwave‑safe.”

When it’s (probably) okay

Some Styrofoam‑like containers are made from microwave‑safe polystyrene and are tested by regulators such as the U.S. FDA.

Look for:

  • A microwave‑safe symbol (often a microwave icon with wavy lines).
  • Words like “microwave safe” printed on the bottom or side.

If you see that label, short‑term reheating on medium power is generally considered low‑risk.

Why regular Styrofoam is risky

Most takeout boxes, coffee cups, and foam trays are not meant for microwave heat.

Risks include:

  • Melting or warping , which can spill hot food and cause burns.
  • Chemicals leaching , especially styrene , a compound linked in some studies to cancer at high exposures.
  • Higher risk with fatty or oily foods (like pizza, fried items, or creamy sauces), which heat more intensely and can pull more chemicals out.

Safer alternatives

If the Styrofoam isn’t labeled microwave‑safe, transfer the food to:

  • Glass or ceramic containers marked microwave‑safe.
  • Microwave‑safe plastic (look for the same symbol).

These options are more stable under heat and usually reusable, which is also better for the environment.

Quick decision table

[1][3] [9][3] [7][3]
Type of Styrofoam Microwave safe? What to do
Labeled “microwave‑safe” or has microwave icon Yes, with caution Use short times, medium power, and avoid very fatty foods.
Unlabeled takeout box or foam cup No Transfer food to glass, ceramic, or labeled plastic instead.
Old, cracked, or stained Styrofoam No Do not microwave; risk of melting and chemical release is higher.

If you accidentally microwave Styrofoam

If you briefly microwaved unlabeled Styrofoam and it didn’t melt or smell strongly, the risk from a single incident is likely low, but it’s still best to avoid repeating it.

If the container warped, bubbled, or smells “plasticky,” discard both the container and the food.

Information gathered from public forums or data available on the internet and portrayed here.