Styrofoam containers are a staple of takeout meals and leftovers storage. Their lightweight design makes them easy to carry while keeping food insulated and at the proper temperature.
However, when it comes time to reheat your meal, you may be wondering if it’s safe to microwave that styrofoam container. After all, you’ve probably heard warnings about the dangers of putting styrofoam in the microwave.
But is 30 seconds really long enough to cause a problem? Let’s take a closer look at the risks and safety precautions around microwaving styrofoam.
What Happens When Styrofoam is Microwaved?
Styrofoam is made from polystyrene, a type of plastic. When exposed to the high heat inside a microwave oven, the molecules that make up the styrofoam container begin vibrating rapidly. As they vibrate, the bonds holding the molecules together start to break down.
This molecular deterioration causes the styrofoam to partially melt or deform when microwaved. Higher temperatures and longer cooking times increase the likelihood and severity of melting. At certain temperatures, usually around 250°F, the styrofoam can start emitting toxic fumes.
Dangers of Microwaved Styrofoam
So what exactly is the danger in microwaving styrofoam? Here are some of the potential risks:
1. Chemical leaching
Heating polystyrene foam releases compounds that may migrate into food. Two primary chemicals released are the monomer styrene and benzene derivatives. Styrene exposure is concerning, as epidemiological studies have observed associations between high styrene levels and both nervous system dysfunction and several cancer types.
Benzene derivatives are also worrisome, as they exhibit mutagenic and carcinogenic properties in lab studies. While no defined safety threshold exists, it’s plausible that repetitive exposure to even low doses of styrene and benzene from heated foam carries long-term health risks. Prudent avoidance of microwaving polystyrene foam when alternative heat-resistant containers are available is advisable.
2. Burn hazards
Hot, melting styrofoam can easily cause burns if it drips onto your skin when removing the container from the microwave. The Food and Drug Administration (FDA) has warned that microwaved styrofoam containers can become very hot—up to 250°F!
At high enough temperatures, melted styrofoam could potentially catch fire, creating a very dangerous situation. This is especially true if there are any metal components like aluminum foil or twist ties included.
3. Difficulty gauging temperature
When styrofoam melts during microwaving, it’s nearly impossible to accurately gauge the true temperature of your food. The insulation properties of the styrofoam are lost. Parts of the food could end up severely overheated even though the container feels cool to the touch. This could lead to accidental burns in your mouth.
4. Loss of structural integrity
As styrofoam loses its shape and solidity, your food is no longer fully protected. Spills, leaks, and collapses become more likely. Hot liquid foods like soup or oatmeal could more easily soak through a distorted container onto your hands, lap, or counter.
Is 30 Seconds Enough to Cause Damage?
Most experts agree that limited exposure to microwave radiation, such as 30 seconds or less, is unlikely to melt or damage styrofoam significantly. However, there are a few factors to keep in mind:
- Power level – The higher the power level on your microwave, the faster heat builds up. A 30-second blast at 80% power could get a container hotter than 30 seconds at a lower power.
- Spacing – Stacked containers heat faster since more surfaces absorb energy. If microwaved alone with space around it, 30 seconds may be OK.
- Fill level – The more food or liquid in the container, the more evenly heat will distribute rather than focusing on the container itself. Deeply filled containers tend to heat styrofoam less.
- Container thickness – Thin containers designed for limited utility (like cups or trays) may deform easier under heat than thick, heavy-duty storage containers.
- Ventilation – Some microwaves have ventilation systems that prevent excessive heat buildup. Well-ventilated ovens disperse heat faster than cheap models.
While the risks from very brief exposure are much lower, it’s still smart to minimize microwave time for styrofoam as much as possible. The safest option is always to transfer food into a microwave-safe dish before heating.
Signs of Damage in Styrofoam
Sometimes even 30 seconds in the microwave is enough to cause subtle changes to styrofoam that indicate the container shouldn’t be used again. Here’s what to look for:
- Deformation – Sagging, slumping, or warping shows the structure has been compromised. Molten plastic can also fuse items together.
- Discoloration – Look for new yellowing, browning, or black marks. This indicates chemical changes have occurred.
- Softening – Styrofoam will normally feel rigid and brittle to the touch. If areas feel softened or rubbery, the foam cells have melted.
- Cracking – Fissures, fractures, and peeling mean bonds have weakened and small failures have happened.
- Residue – Be suspicious of any oily sheen or sticky black/brown residue left on the food. This could be melted plastic or chemical deposits.
Discard any styrofoam showing these warning signs after microwaving so you don’t risk using a damaged container. Never re-use single-use styrofoam cups, trays, or bowls after microwaving either.
Safe Microwaving Tips for Styrofoam
When working within styrofoam’s limitations, it can be moderately microwave-safe for short durations. Here are some tips to reduce risks:
- Read labels – Use only styrofoam labeled “microwave-safe.” Otherwise assume it’s unsafe.
- Follow instructions – Adhere to any power level, time limit, or other usage directions.
- Transfer food – For longer cook times, transfer food into microwave-safe dishware first.
- Elevate containers – Use a microwave-safe stand or inverted plate to prevent direct contact with the turntable.
- Leave room – Arrange multiple containers so they’re not touching or stacked. Leave space around them.
- Cover food – Having another microwave-safe plate or paper towel covering food helps prevent splatters on the styrofoam.
- Ventilate – Open microwave door periodically to allow steam and heat to escape, especially for foods with high-water content.
- Check condition – Inspect for damage after use and discard if any is found. Do not re-use single-use products.
When to Avoid Microwaving Styrofoam
There are certain situations when it’s always smart to avoid putting styrofoam in the microwave:
- You need to heat food for more than 30-60 seconds total.
- The styrofoam is thin, flimsy, or seems cheaply made.
- You’ve microwaved the container before, increasing likelihood of damage.
- The food inside has high oil or sugar content that could melt plastic faster.
- You see metal components like foil, twist ties, etc. that could spark.
- The container has become stained or is warped/degraded.
- You lack ventilation in the microwave to disperse building heat effectively.
For these higher-risk scenarios, transfer food out of styrofoam into proper microwave-safe dishware instead. Any extra time spent avoids potentially hazardous results later. You can still use the styrofoam to keep foods cold in the fridge or insulated for travel. Just hold off on microwaving those containers.
The Takeaway on 30-Second Microwaving
It’s understandable to be cautious about putting styrofoam in the microwave considering all the warnings. However, current evidence suggests brief microwaving for 30 seconds or less is fairly low-risk if the container is in good condition and used properly.
That being said, it’s impossible to guarantee “complete safety.” Trace amounts of chemicals could possibly leach out even during short exposures. Higher fat/sugar foods may absorb more than water-based items. The safest recommendation is always to transfer food out of styrofoam prior to extended microwaving.
For quickly reheating a food or beverage for 30 seconds or less, styrofoam should remain generally intact and safe to touch. But inspect carefully afterward for any signs of damage like softening or deformity. Any changes mean the container took on more heat than it was designed to withstand. When in doubt, throw it out to avoid potential health hazards.
With proper precautions, brief microwaving won’t outright melt most styrofoam containers. Yet, it’s smart to use ceramic, glass, or paper products labeled microwave-safe whenever possible. Limit any styrofoam exposure to the bare minimum needed to get your food warm enough to enjoy.