Number 5 plastic, also known as polypropylene (PP), is one of the safest plastics available for food contact. It’s approved by both the FDA and EPA for single and repeated use with food, and it does not contain BPA or phthalates, two chemicals that have drawn the most concern in plastic safety discussions. That said, “safe” comes with some important nuances worth understanding.
What Makes Number 5 Plastic Different
The recycling number on the bottom of a plastic container tells you what type of plastic it’s made from. Number 5 is polypropylene, a lightweight, heat-resistant plastic used in yogurt cups, deli containers, medicine bottles, bottle caps, and reusable food storage containers. It has a higher melting point than most consumer plastics, which is why it’s the type most often labeled microwave-safe.
Unlike number 7 plastic (polycarbonate), polypropylene is not made with bisphenol A. It also doesn’t contain phthalates, the softening chemicals found in some flexible plastics like PVC. These two facts are the main reasons polypropylene has a strong safety reputation relative to other plastics.
What the Research Actually Shows
Polypropylene’s regulatory approval is solid, but newer research paints a more complicated picture of plastic safety in general. A study published in the journal Environmental Science & Technology tested 24 everyday plastic products across eight different polymer types, including polypropylene, and found that every single product leached chemicals that triggered toxic responses in lab-based cell tests. The researchers identified nearly 3,000 unique compounds migrating from the products they tested, and estimated that represented only about 8% of all the chemical features they detected. Most of the chemicals leaching from these plastics remain unidentified and unstudied.
One of the study’s key findings was that toxicity depended more on the specific product than on the type of plastic. Two polypropylene containers from different manufacturers could have very different chemical profiles because of the additives, colorants, stabilizers, and processing aids used during production. The base polymer might be safe, but the finished product is a more complex question.
Heat, Microwaving, and Leaching
Heat accelerates chemical migration from any plastic into food or liquid. Polypropylene handles heat better than most plastics, but “better” is relative. Research on polypropylene baby bottles found that preparing infant formula with boiling water released more than 40 times the amount of microplastic particles compared to room-temperature use. This finding has contributed to a decline in polypropylene baby bottles on the market.
For everyday use, only microwave containers that carry a specific microwave-safe symbol, which is typically a set of wavy lines or an image of a microwave. The recycling number alone doesn’t confirm microwave safety. A number 5 container that’s designed for cold deli storage is not the same as one engineered to handle repeated reheating. Avoid microwaving food in any plastic container that’s scratched, stained, or warped, as surface degradation increases the potential for chemical migration.
Dishwasher and Long-Term Use
The recycling symbol and the dishwasher-safe symbol are two different things. The number inside the triangle of arrows identifies the plastic type. A dishwasher-safe symbol looks like small plates or circles with water droplets or diagonal lines above them. If the water lines appear only above the plates, the item should go on the top rack only. If the lines surround the entire image, it’s safe for either rack.
Most plastic containers, including polypropylene, should be placed on the top rack of the dishwasher regardless, where temperatures are lower. The bottom rack sits closer to the heating element and can warp plastics or accelerate surface wear. Discard containers that have become scratched, cloudy, or warped over time. Damaged surfaces can harbor bacteria and may release more chemicals during use.
A Note on Baby Products
The FDA’s approval of polypropylene for food contact is broad, covering everything from cold storage to hot-fill applications. However, certain FDA clearances for polypropylene specifically exclude contact with infant formula and human milk. This doesn’t mean all polypropylene baby products are unsafe, but it does reflect a more cautious regulatory approach for infants, whose smaller body weight makes them more vulnerable to any chemical exposure. If you’re choosing bottles or milk storage bags, look for products that have been individually tested and cleared for infant use rather than assuming the plastic type alone guarantees safety.
How to Minimize Risk
- Reduce heat exposure. Transfer food to glass or ceramic before microwaving when possible. If you do microwave in plastic, use only containers with a microwave-safe label.
- Replace worn containers. Scratches, cloudiness, and warping are signs the plastic is degrading. Swap them out.
- Don’t store hot food in plastic. Let leftovers cool before sealing them in a polypropylene container.
- Use glass for liquids. Water bottles and food storage containers made of glass eliminate plastic leaching entirely.
Polypropylene remains one of the better choices if you’re going to use plastic. It’s free of the most well-known problem chemicals and holds up to heat better than alternatives. But no plastic is completely inert, and the safest approach is to limit how often hot food or liquids sit in any plastic container for extended periods.