Dear Science,

On a daily basis, I store food in, heat food up in, and eat food out of plastic Tupperware, specifically Ikea and Glad brands. The resin ID code is 5 on at least one of them, meaning it's made of polypropylene (thanks, Wikipedia). Is this type of plastic food container actually safe for daily use, especially reheating meals? Are any possible deleterious effects simply negligible?

Maybe At Risk, But Fed

Your question touches on a deeply controversial area right now. If you are Canadian or a citizen of the EU, the official answer would be "Yes, these food containers probably leach out chemicals that could have deleterious health effects." If you are an American, the official answer would be "Hell no! Eat up."

Like all plastics, polypropylene is made up of long chains of repeating simple molecules. The simple molecule here, the monomer of polypropylene, is a three-carbon molecule—two carbons in the chain with a methyl group hanging off. The monomer is somewhat toxic to people. By the time these tiny molecules are linked into gigantic chains, the material is inert. The controversy arises with the other molecules added to the plastic, in tiny quantities, to change the flexibility, transparency, UV resistance, and such of the final material.

The (potential) problems with these additives were found by accident. Polypropylene is resistant to a wide variety of chemicals and thus is frequently used to make laboratory tools—like beakers and pipettes for transferring tiny amounts of liquid. Using a variety of lab tools made of polypropylene, biologists at the University of Alberta were experimenting on enzymes found in humans—specifically, an enzyme found in human brains called MAO-B, involved in the processing of the neurotransmitter dopamine. The results made no sense. Rather than blaming the responsible graduate students, the lab fired up a mass spectrometer and dug deeper. A paper published in the journal Science in 2008 describes what they found: Some of the additives—oleamide, used to change the texture of the plastic, and DiHEMDA, used as an antimicrobial—in the polypropylene plasticware were leaching out and disrupting the function of human MAO-B. (MAO-inhibiting drugs are among the most potent psychoactive medicines.) After washing the plastic extensively, the additives no longer disrupted the experiments.

There arises the concern. Quite a few foods are shipped and stored in polypropylene. Just like these additives leaked out and disrupted the scientists' experiments, they could (in theory) leach out into the food and affect the same enzymes in your brain. As demonstrated by the scientists washing their plasticware and reducing these effects, your old (and heavily washed) Tupperware is probably safe at this point. Yogurt containers, fresh from the factory when filled, are another story.

For now, Science recommends storing and heating food in glass.

Adulteratingly yours,


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This article has been updated since its original publication.